Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy

Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy Yongli Dai, jialin Cao, Mengchun Wang, Dandan Zhang, Juntao Pan, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9073140/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Objective Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising non-invasive neuromodulation therapy for post-stroke neurological dysfunction, but its neurophysiological mechanism in improving oral phase dysphagia remains unclear. This study aimed to investigate the effects of taVNS combined with routine swallowing rehabilitation on swallowing function and cortical activation patterns in patients with post-stroke oral phase dysphagia using functional near-infrared spectroscopy (fNIRS), and to elucidate the potential neuromodulatory mechanism of taVNS. Methods A single-blind, randomized controlled trial was conducted on 40 patients with post-stroke oral phase dysphagia admitted to our hospital from July 2023 to January 2025. Patients were randomly assigned to the conventional Therapy group (n = 20, sham taVNS + routine swallowing rehabilitation) and the taVNS group (n = 20, real taVNS + routine swallowing rehabilitation) at a 1:1 ratio via lottery. The intervention lasted for 2 weeks (5 sessions/week, 30 min/session for rehabilitation, 25 min/session for taVNS). Swallowing function was assessed using the Standardized Swallowing Assessment (SSA), Oral Function Scale (OFS), and Swallowing-Quality of Life (SWAL-QOL) scale before and after intervention by the same blinded evaluator. fNIRS was used to detect cortical hemodynamic responses (oxyhemoglobin, HbO) during chewing and tongue tip sliding tasks, and the activation levels of the prefrontal cortex (PFC), premotor/supplementary motor cortex (PM), primary motor cortex (M1), and primary somatosensory cortex (S1) were quantified. NIRS-KIT and SPSS 27.0 were used for fNIRS data processing and statistical analysis, respectively. Results There were no significant differences in baseline clinical characteristics and swallowing function scores between the two groups (all p > 0.05). After intervention, both groups showed significant improvements in SSA and OFS scores (all p < 0.05); the taVNS group had a significant increase in SWAL-QOL scores ( p 0.05). Intergroup comparison showed no significant differences in SSA and SWAL-QOL scores ( p > 0.05), but the taVNS group had significantly higher OFS scores than the conventional group ( p < 0.05). For fNIRS results, in the chewing task, both groups exhibited significantly enhanced activation in the right PFC (RPFC), left PM (LPM), and left M1 (LM1) after intervention (all p < 0.05), and the taVNS group had significantly stronger LPM activation than the conventional group ( p < 0.05). In the tongue tip sliding task, both groups showed significant activation enhancement in LPM, right PM (RPM), LM1, and right S1 (RS1) (all p < 0.05); additionally, the taVNS group had significant activation increases in right M1 (RM1) and left S1 (LS1) ( p 0.05). No severe adverse events were observed in either group during the intervention. Conclusion taVNS combined with routine swallowing rehabilitation is safe and effective for post-stroke oral phase dysphagia, and has a superior effect on improving oral motor function compared with routine rehabilitation alone. The neurophysiological mechanism of taVNS may be related to the enhancement of LPM activation and the promotion of extensive bilateral activation in M1 and S1, which optimizes the activation intensity and pattern of the central swallowing motor-related cortex, thereby facilitating the recovery of oral phase swallowing function. A schematic diagram illustrating this proposed neurophysiological mechanism is presented in Fig. 6. Stroke Oral phase dysphagia Transcutaneous auricular vagus nerve stimulation Functional near-infrared spectroscopy Cortical activation Neuromodulation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Dysphagia is a common and debilitating complication after stroke, with a prevalence ranging from 50% to 80% in acute and recovery phases [ 1 ]. Among them, oral phase dysphagia accounts for approximately 40% of post-stroke dysphagia cases [ 2 ], characterized by impaired mastication, tongue movement dysfunction, and oral residue, which not only leads to malnutrition and dehydration but also increases the risk of aspiration pneumonia, significantly reducing patients’ quality of life and increasing medical burdens [ 3 ]. The oral phase of swallowing is a complex voluntary motor process regulated by a network of cerebral cortical regions, including the primary motor/somatosensory cortex (M1/S1), premotor/supplementary motor cortex (PM), and prefrontal cortex (PFC) [ 4 ]. Stroke-induced damage to this cortical network leads to abnormal neural activation and impaired neural plasticity, which is the core neurophysiological basis of oral phase dysphagia [ 5 ]. Routine swallowing rehabilitation (e.g., sensory stimulation, motor training) is the first-line treatment for post-stroke dysphagia, which can improve peripheral swallowing muscle function through the "peripheral-central" feedback pathway [ 6 ]. However, its effect on reversing central cortical network dysfunction is limited, and a considerable number of patients still have persistent swallowing impairment [ 7 ]. In recent years, non-invasive neuromodulation therapies have become a research hotspot for improving post-stroke neurological dysfunction by regulating cortical neural plasticity. Transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) have been applied in the treatment of post-stroke dysphagia [ 8 ], but their clinical application is restricted by high cost, strict operational requirements, and limited stimulation coverage. Transcutaneous auricular vagus nerve stimulation (taVNS), as a novel non-invasive neuromodulation technology, stimulates the auricular branch of the vagus nerve in the cymba conchae, which can ascend to activate the vagal afferent nucleus, thalamus, and multiple cerebral cortical regions [ 9 ]. It has the advantages of simplicity, low cost, and wide cortical stimulation coverage, and has been proven to improve motor and cognitive function in stroke patients [ 10 , 11 ]. A recent clinical study found that taVNS combined with routine rehabilitation can improve post-stroke dysphagia [ 12 ], but its specific effect on the oral phase and the underlying cortical activation mechanism remain unclear, which limits its personalized clinical application. Functional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technology that reflects cortical neural activity by detecting changes in oxyhemoglobin (HbO) concentration based on the neurovascular coupling mechanism [ 13 ]. Compared with functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), fNIRS has the advantages of high portability, low motion artifact sensitivity, and compatibility with clinical motor tasks [ 14 ], making it an ideal tool for real-time detection of cortical activation during swallowing motor tasks. In recent years, fNIRS has been widely used to explore the cortical mechanism of swallowing and the therapeutic effect of neuromodulation therapies [ 15 , 16 ]. Previous fNIRS studies have confirmed that M1, S1, PM, and PFC are the core brain regions regulating the oral phase swallowing tasks (e.g., mastication, tongue movement) [ 4 ], and the recovery of post-stroke dysphagia is closely related to the reconstruction of the activation pattern of these brain regions [ 17 ]. However, there are few studies on the changes in cortical activation of taVNS for post-stroke oral phase dysphagia detected by fNIRS. This study adopted a randomized controlled design to compare the effects of taVNS combined with routine swallowing rehabilitation and sham taVNS combined with routine rehabilitation on the swallowing function of patients with post-stroke oral phase dysphagia. fNIRS was used to detect the cortical activation changes of the core swallowing-related brain regions (PFC, PM, M1, S1) during two typical oral phase swallowing tasks (chewing and tongue tip sliding). We hypothesized that taVNS could enhance the activation of swallowing-related cortical regions and optimize the bilateral activation pattern, thereby improving oral phase swallowing function. The results of this study will provide neurophysiological evidence for the clinical application of taVNS in post-stroke oral phase dysphagia and lay a foundation for the development of personalized neuromodulation rehabilitation programs. 2. Methods 2.1 Study design and participants This was a single-blind, randomized controlled trial approved by the Ethics Committee of the Second Affiliated Hospital of Dalian Medical University (KY2025-105-01) and conducted in accordance with the Declaration of Helsinki. A total of 40 patients with post-stroke oral phase dysphagia were recruited from the Rehabilitation Medicine Department of our hospital from July 2023 to January 2025. Inclusion criteria : ① Met the diagnostic criteria for cerebral hemorrhage or cerebral infarction formulated by the Fourth National Cerebrovascular Disease Academic Conference of the Chinese Medical Association [ 18 ], and confirmed by cranial computed tomography (CT) or magnetic resonance imaging (MRI); ② Unilateral lesion, first onset, and onset time of 7 days to 1 month; ③ Grade 2–5 on the Water Swallowing Test(WST), with typical clinical manifestations of oral phase dysphagia (e.g., impaired mastication, tongue movement disorder); ④ Aged 30–70 years; ⑤ No obvious cognitive impairment (Mini-Mental State Examination, MMSE: illiterate > 17 points, primary school > 20 points, junior high school and above > 24 points); ⑥ Signed informed consent voluntarily. Exclusion criteria ① Skull defect; ② Tracheostomy status; ③ Ineligible for auricular electrical stimulation (e.g., auricular infection, ulcer, scar); ④ Resting heart rate < 60 beats/min; ⑤ Implanted medical devices such as cardiac pacemaker and cochlear implant; ⑥ A history of vagus nerve surgery; ⑦ A history of oral and maxillofacial surgery or structural dysfunction of the oral and maxillofacial region; ⑧ Other neurological or muscular diseases interfering with assessment (e.g., oral fibrosis, masticatory muscle atrophy). Patients were randomly assigned to the conventional Therapy group and the taVNS group at a 1:1 ratio using the lottery method. The evaluators of swallowing function and fNIRS data analysts were blinded to the group assignment, and the patients were unaware of the type of stimulation (real/sham). 2.2 Interventional protocols Both groups received 2 weeks of routine swallowing rehabilitation (5 sessions/week, 1 session/day, 30 min/session), and the taVNS intervention (real/sham) was performed 30 minutes before each rehabilitation session, with a duration of 25 min/session. 2.2.1 Routine swallowing rehabilitation The rehabilitation program was formulated by professional rehabilitation therapists and included the following components: ① Acid stimulation: Diluted acidic liquids (lemon juice/vinegar) were used to stimulate the tongue and oral mucosa; ② Ice stimulation: Ice cubes were used to gently stimulate the pharynx, neck, and tongue body; ③ Vibration sensory stimulation: A vibration rod was used for mild vibration stimulation of the pharynx and jaw; ④ Pharyngeal swallowing muscle massage: Manual massage of the pharyngeal and laryngeal muscles; ⑤ Swallowing motor training: Facial muscle training (pursed lips, teeth showing, cheek puffing) and tongue muscle resistance training (tongue retractor traction of the anterior tongue). 2.2.2 taVNS intervention A low-frequency pulsed electrical stimulator (En-stim4, Shanghai Xibei Electronic Technology Development Co., Ltd., China) with biphasic pulsed current mode was used for both real and sham taVNS. The stimulation parameters were consistent: pulse frequency 25 Hz, pulse width 0.5 ms, 30 s stimulation with 30 s interval, and the current intensity was adjusted to 0.1 mA below the pain threshold. taVNS group (real stimulation) : The left cymba conchae (the innervation area of the auricular branch of the vagus nerve) was routinely disinfected, and the electrodes were placed on the left cymba conchae for electrical stimulation. Conventional Therapy group (sham stimulation) : The left earlobe (non-innervation area of the auricular branch of the vagus nerve) was routinely disinfected, and the electrodes were placed on the left earlobe for electrical stimulation with the same parameters as the taVNS group. 2.3 Outcome assessments All assessments were completed by the same trained rehabilitation evaluator before intervention (baseline) and immediately after 2 weeks of intervention. The assessment indicators included swallowing function scales and fNIRS cortical activation detection, and safety assessment was performed during the entire intervention period. 2.3.1 Swallowing function scale assessment Standardized Swallowing Assessment (SSA) : A reliable and valid scale for evaluating swallowing function, including clinical examination (8–23 points), 5 ml warm water swallowing test (5–11 points), and 60 ml warm water swallowing test (5–12 points), with a total score of 18–46 points. A higher score indicates worse swallowing function [ 19 ]. Oral Function Scale (OFS) : A scale for evaluating oral motor function in dysphagia patients, including 7 items such as mastication, swallowing, and tongue flexibility. Each item is scored as 1 (unable to perform), 2 (needing assistance/modification), and 3 (able to perform independently), with a total score ranging from 7 to 21 points. A higher score indicates better oral function [ 20 ]. Swallowing-Quality of Life (SWAL-QOL) : A specific scale for evaluating the quality of life of dysphagia patients, including 44 items covering 11 dimensions (8 swallowing-related dimensions: psychological burden, eating time, appetite, food choice, verbal communication, fear of eating, mental health, social interaction; 2 general dimensions: fatigue, sleep; 1 dysphagia frequency dimension). Each item is scored on a 5-point Likert scale (1–5 points), with a higher total score indicating a better quality of life related to swallowing [ 21 ]. 2.3.2 fNIRS detection fNIRS device and probe placement : A 35-channel fNIRS system (Huichuang Medical Equipment Co., Ltd., Danyang, China) with two near-infrared wavelengths (730 nm and 850 nm) was used to detect the changes in HbO and deoxyhemoglobin (HbR) concentrations in the cerebral cortex. The probe cap included 14 light sources and 14 detectors, with a probe spacing of approximately 3 cm, forming 35 detection channels. The probe cap was placed according to the international 10–20 system, and the target regions of interest (ROIs) included the left/right PFC, left/right PM, left/right M1, and left/right S1. The channel positions corresponding to each ROI were determined based on the Brodmann atlas (Fig. 1 ). Task paradigm : All patients completed two oral phase swallowing motor tasks in a quiet and comfortable environment: chewing task (simulating mastication at a daily eating frequency) and tongue tip sliding task (sliding the tongue tip along the hard palate backward at a voluntary rhythm). Each task adopted a block design: 3 rest blocks and 3 task blocks, with each block lasting 30 s. A 30 s resting state data was collected before the start of the task and after each task block (patients kept relaxed, sitting still, and avoiding thinking). The total duration of each task was 210 s, and a 1-minute rest was given between the two tasks to avoid fatigue. fNIRS data processing : fNIRS data was processed using the NIRS-KIT toolbox based on MATLAB R2021a (MathWorks, USA), following the standard processing pipeline [ 22 ]: ① Converting raw light intensity data into HbO and HbR concentrations based on the Beer-Lambert law; ② Previewing and removing obvious bad channels; ③ Eliminating linear drift using a polynomial regression model; ④ Correcting motion artifacts using the temporal derivative distribution repair method; ⑤ Band-pass filtering (0.01–0.08 Hz) using a third-order Butterworth filter. Considering the higher signal-to-noise ratio of HbO compared with HbR [ 13 ], only HbO data was used for subsequent cortical activation analysis. Cortical activation quantification : A general linear model (GLM) based on the hemodynamic response function (HRF) was used to model the task-related hemodynamic activity of each channel at the individual level, and the β value (regression coefficient) of each channel was calculated to reflect the cortical activation intensity. The average β value of all channels in each ROI was taken as the activation intensity of the corresponding brain region [ 16 ]. 2.3.3 Safety assessment Blood pressure, pulse, and heart rate of patients were measured using a sphygmomanometer and stethoscope before and after each taVNS (real/sham) intervention to evaluate the risk of cardiac adverse reactions. After each intervention, patients were asked about subjective discomfort (e.g., auricular pain, burning sensation, dizziness), and the occurrence of adverse events was recorded in detail. 2.4 Statistical analysis All data were collated using Microsoft Excel 2021 and statistically analyzed using SPSS 27.0 (IBM, USA) and G*Power 3.1. Measurement data were expressed as mean ± standard deviation (Mean ± SD) after verifying normality via the Shapiro-Wilk test and homogeneity of variance via Levene’s test. Sample size calculation was performed a priori based on the primary outcome (Oral Function Scale [OFS] score): assuming an effect size f = 0.25, significance level α = 0.05, and statistical power 1 − β = 0.80, the calculation indicated that 34 participants (17 per group) were required to detect significant between-group differences. Considering a potential 20% dropout rate, 40 participants (20 per group) were enrolled, ensuring sufficient statistical power for core outcomes. Intragroup comparisons of baseline and post-intervention data were performed using paired samples t -test, and intergroup comparisons of post-intervention data were conducted using independent samples t -test. Repeated-measures analysis of variance (RM-ANOVA) was further used to confirm the interaction effect of "group × time" (with age and stroke type as covariates), The interaction effect of 'group × time' was significant for OFS score (F = 4.89, p = 0.032) and LPM activation (F = 5.12, p = 0.028), confirming that the therapeutic effect of taVNS was independent of age and stroke type,and the results were consistent with t -test findings (all p 0.8 was considered a large effect, 0.5–0.8 a medium effect, and 0.2–0.5 a small effect. Count data were expressed as percentage (%), and comparisons were performed using the chi-square test. P < 0.05 was considered statistically significant. 3. Results 3.1 Baseline clinical characteristics A total of 40 patients were enrolled in the study, with 20 patients in each group, and all completed the intervention and assessments (no dropout). There were no significant differences in baseline clinical characteristics (age, gender, stroke type, affected hemisphere) and swallowing function scores (SSA, OFS, SWAL-QOL) between the two groups (all p > 0.05), indicating good group balance (Table 1 ). Table 1 Comparison of baseline clinical characteristics between the two groups (Mean ± SD) Index Conventional Therapy group (n = 20) taVNS group (n = 20) t /χ² value p value Age (years) 58.67 ± 8.96 56.79 ± 8.05 0.702 0.483 Gender (male:female, n) 14:6 13:7 0.119 0.743 Stroke type (ischemic:hemorrhagic, n) 13:7 15:5 0.457 0.502 Affected hemisphere (left:right, n) 12:8 11:9 0.109 0.756 Standardized Swallowing Assessment (SSA) total score 23.33 ± 1.72 23.23 ± 2.42 0.121 0.905 Oral Function Scale (OFS) total score 5.157 ± 2.627 4.861 ± 2.877 0.320 0.444 Swallowing-Quality of Life (SWAL-QOL) total score 121.42 ± 4.94 119.31 ± 8.07 0.901 0.361 Note: Data are presented as Mean ± SD. Continuous variables were compared using independent samples t-test, and categorical variables using chi-square test. No significant differences were observed between groups at baseline (all p > 0.05). 3.2 Changes in swallowing function scale scores After 2 weeks of intervention, the swallowing function scores of the two groups showed different degrees of improvement, and the intragroup and intergroup comparison results were as follows (Tables 2 – 4 ): SSA score : Both groups had significantly lower SSA scores after intervention compared with baseline (conventional group: t = 2.983, p = 0.007; taVNS group: t = 2.978, p = 0.007), with no significant intergroup difference in post-intervention SSA score ( t = 0.852, p = 0.403). OFS score : Both groups had significantly higher OFS scores after intervention compared with baseline (conventional group: t =-3.478, P = 0.001; taVNS group: t =-3.038, p = 0.004). The post-intervention OFS score of the taVNS group was significantly higher than that of the conventional group ( t =-3.451, p = 0.001). SWAL-QOL score : The taVNS group had a significantly higher SWAL-QOL score after intervention compared with baseline ( t =-3.029, p = 0.006), while the conventional group had no significant change ( t =-1.152, p = 0.262). There was no significant intergroup difference in post-intervention SWAL-QOL score ( t =-1.487, p = 0.151). Table 2 Comparison of Standardized Swallowing Assessment (SSA) total scores between the two groups before and after intervention (Mean ± SD) Group n Baseline Post-intervention t value p value Effect size(Cohen’s d) Conventional Therapy 20 23.333 ± 1.723 21.333 ± 1.557 2.983 0.007 1.12 taVNS 20 23.231 ± 2.421 20.769 ± 1.739 2.978 0.007 1.08 t value (intergroup) 0.121 0.852 P value (intergroup) 0.905 0.403 Note: SSA total score ranges from 18 to 46, with higher scores indicating worse swallowing function. Intragroup comparisons were performed using paired samples t-test. Both groups showed significant improvement after intervention (both p 0.05). Cohen’s d > 0.8 indicates a large effect size, 0.5–0.8 a medium effect, and 0.2–0.5 a small effect. Table 3 Comparison of Oral Function Scale (OFS) total scores between the two groups before and after intervention (Mean ± SD) Group n Baseline Post-intervention t value p value Effect size(Cohen’s d) Conventional Therapy 20 4.712 ± 1.456 6.312 ± 1.454 -3.478 0.001 0.97 taVNS 20 4.561 ± 2.877 8.231 ± 1.684 -3.038 0.004 1.35 t value (intergroup) 0.581 -3.451 P value (intergroup) 0.561 0.001 Note: OFS total score ranges from 7 to 21, with higher scores indicating better oral motor function. Intragroup comparisons were performed using paired samples t-test, and intergroup comparison using independent samples t-test. Both groups showed significant improvement after intervention (both p < 0.01), and the taVNS group had a significantly higher score than the conventional group ( p < 0.01) with a large effect size (d = 1.35). Table 4 Comparison of Swallowing-Quality of Life (SWAL-QOL) total scores between the two groups before and after intervention (Mean ± SD) Group n Baseline Post-intervention t value p value Effect size(Cohen’s d) Conventional Therapy 20 121.417 ± 4.944 124.167 ± 6.631 -1.152 0.262 0.45 taVNS 20 119.308 ± 8.077 128.154 ± 6.756 -3.029 0.006 1.21 t value (intergroup) 0.779 -1.487 P value (intergroup) 0.444 0.151 Note: SWAL-QOL total score ranges from 32 to 160, with higher scores indicating better swallowing-related quality of life. Intragroup comparisons were performed using paired samples t-test. Only the taVNS group showed significant improvement after intervention ( p 0.05). 3.3 Changes in fNIRS cortical activation 3.3.1 Chewing task At baseline, there was no significant difference in the activation intensity of all ROIs between the two groups (all p > 0.05). After intervention, both groups showed significant activation enhancement in RPFC, LPM, and LM1 compared with baseline (all p < 0.05; Fig. 2 ). Intergroup comparison of post-intervention activation intensity showed that the taVNS group had significantly stronger LPM activation than the conventional group (Mean ± SD: 0.71 ± 0.16 vs. 0.47 ± 0.14, p 0.05; Fig. 3 ). 3.3.2 Tongue tip sliding task At baseline, there was no significant difference in the activation intensity of all ROIs between the two groups (all p > 0.05). After intervention, both groups exhibited significant activation enhancement in LPM, RPM, LM1, and RS1 compared with baseline (all p < 0.05). In addition, the taVNS group had significant activation increases in RM1 and LS1 after intervention ( p < 0.05), which was not observed in the conventional group (Fig. 4 ). Intergroup comparison of post-intervention activation intensity showed no significant differences in all ROIs between the two groups (all p > 0.05), but the taVNS group exhibited a more extensive bilateral activation pattern characterized by additional activation of RM1 and LS1 (Fig. 5 ). 3.4 Safety assessment No severe adverse events (e.g., cardiac arrhythmia, severe hypotension, dizziness) were observed in either group during the 2-week intervention. Only 1 patient in the taVNS group reported a mild burning sensation in the left cymba conchae during the first intervention, and the discomfort disappeared after suspending the intervention, cleaning the auricular skin, and appropriately reducing the current intensity. No other subjective discomfort was reported by the patients, and the tolerance of the intervention was good. 4. Discussion This study confirmed that taVNS combined with routine swallowing rehabilitation can safely and effectively improve the oral phase swallowing function of stroke patients, and has a superior effect on enhancing oral motor function compared with routine rehabilitation alone. For the first time, fNIRS was used to clarify the neurophysiological mechanism of taVNS in improving oral phase dysphagia: taVNS can enhance the activation of LPM (a key brain region regulating oral swallowing) and promote extensive bilateral activation of M1 and S1, thereby optimizing the activation pattern of the central swallowing motor cortical network. 4.1 taVNS improves oral phase swallowing function: clinical efficacy analysis Routine swallowing rehabilitation can improve the oral phase swallowing function of stroke patients by stimulating peripheral sensory receptors and training swallowing muscles, which is consistent with the significant improvement of SSA and OFS scores in the conventional group in this study [ 6 ]. However, the conventional group had no significant improvement in SWAL-QOL scores, suggesting that routine rehabilitation only improves objective swallowing motor function, and has a limited effect on patients’ subjective quality of life related to swallowing (e.g., psychological burden, fear of eating). The taVNS group had significant improvements in SSA, OFS, and SWAL-QOL scores, and the OFS score was significantly higher than that of the conventional group, indicating that taVNS can produce an additional therapeutic effect on the basis of routine rehabilitation, especially in improving oral motor function, and also has a positive effect on improving patients’ subjective swallowing quality of life. The superior effect of taVNS on oral motor function may be related to its specific regulation of the oral swallowing motor network. The oral phase of swallowing is a voluntary motor process dominated by the cortical motor system, and PM, M1, and S1 are the core brain regions regulating oral motor functions such as mastication and tongue movement [ 4 ]. taVNS can activate the vagal afferent pathway to regulate the excitability of the cortical motor system [ 9 ], thereby enhancing the neural control of oral swallowing muscles and improving oral motor function (e.g., tongue flexibility, mastication ability), which is reflected in the significant improvement of OFS scores. In addition, taVNS has been proven to regulate the activity of the prefrontal cortex and improve the negative emotions of stroke patients [ 23 ]. The RPFC activation was significantly enhanced in the taVNS group in this study, which may reduce the psychological burden and fear of eating of patients with dysphagia, thus improving the SWAL-QOL score. 4.2 Neurophysiological mechanism of taVNS: analysis of cortical activation changes 4.2.1 Chewing task: enhanced LPM activation is the core of taVNS’s effect Chewing is a typical oral phase swallowing task, which mainly involves the cognitive preparation, motor planning, and executive control of swallowing [ 24 ]. The results of this study showed that both groups had significant activation enhancement in RPFC, LPM, and LM1 after intervention, indicating that routine rehabilitation can also promote the reconstruction of the cortical network related to chewing, which is consistent with previous fNIRS studies [ 15 ]. The key finding of this study is that the taVNS group had significantly stronger LPM activation than the conventional group after intervention, suggesting that enhanced LPM activation is the core neurophysiological basis of taVNS’s additional therapeutic effect. PM is an important brain region connecting the cognitive control and motor execution of swallowing, which receives sensory input from the parietal cortex, integrates motor information, and projects to M1 and spinal motor neurons to regulate the coordination of swallowing muscles [ 25 ]. For stroke patients with unilateral lesion, the damage of the swallowing motor network leads to the decline of PM activation and the loss of motor planning ability, which is an important reason for impaired mastication and uncoordinated tongue movement [ 5 ]. taVNS can increase the release of neurotransmitters (e.g., glutamate, gamma-aminobutyric acid) in the cerebral cortex by activating the vagal afferent pathway, enhance the neural plasticity of the cortical motor system [ 10 ], and thus significantly improve the activation intensity of LPM. The enhanced LPM activation can optimize the motor planning of oral swallowing, improve the coordination of masticatory and tongue muscles, and ultimately lead to the significant improvement of oral motor function, which is consistent with the higher OFS score in the taVNS group. 4.2.2 Tongue tip sliding task: taVNS promotes extensive bilateral activation of M1 and S1 Tongue tip sliding is a key task in the transition from the oral phase to the pharyngeal phase of swallowing, which requires the close cooperation of oral sensory and motor functions, and the bilateral coordination of M1 and S1 is crucial for the smooth completion of this task [ 4 ]. The results of this study showed that both groups had significant activation enhancement in LPM, RPM, LM1, and RS1 after intervention, indicating that routine rehabilitation can promote the activation of the bilateral PM and the sensorimotor cortex related to tongue movement. Notably, the taVNS group also had significant activation increases in RM1 and LS1 after intervention, showing a more extensive bilateral activation pattern of M1 and S1, which is another important neurophysiological mechanism of taVNS’s effect. Post-stroke brain damage leads to the imbalance of the bilateral sensorimotor cortex and the loss of bilateral coordination, which is the main reason for the disorder of tongue movement and the difficulty in the transition from oral to pharyngeal phase [ 17 ]. A previous fNIRS study confirmed that the recovery of post-stroke dysphagia is closely related to the reconstruction of the bilateral activation pattern of the swallowing-related sensorimotor cortex [ 26 ]. taVNS has a wide range of cortical stimulation effects, which can not only activate the affected side cortex but also regulate the excitability of the unaffected side cortex [ 11 ], thereby promoting the reconstruction of the bilateral balance of the sensorimotor cortex. The extensive bilateral activation of M1 and S1 in the taVNS group can enhance the sensory and motor integration of tongue movement, improve the flexibility and coordination of the tongue, and facilitate the smooth transition from the oral phase to the pharyngeal phase of swallowing. Although there was no significant intergroup difference in the activation intensity of all brain regions in the tongue tip sliding task, the more extensive bilateral activation pattern in the taVNS group is an important neurophysiological basis for its long-term therapeutic effect, which needs to be verified by follow-up studies with a longer intervention period. 4.3 Safety and clinical implications of taVNS In this study, taVNS had good safety and tolerance, with only one case of mild auricular burning sensation, which was relieved after simple intervention. No cardiac or neurological adverse events were observed, which is consistent with previous clinical studies on taVNS [ 12 , 23 ]. The selection of the left cymba conchae as the stimulation site is the key to ensuring safety, because the left vagus nerve has a weaker cardiac vagal effect, which can avoid the risk of bradycardia and hypotension [ 9 ]. The stimulation parameters (25 Hz, 0.5 ms pulse width) used in this study are conventional clinical parameters, which have been proven to be safe and effective in previous taVNS studies for stroke [ 10 ], and can be directly applied to clinical practice. The clinical implications of this study are significant: ① taVNS is a safe and effective adjuvant therapy for post-stroke oral phase dysphagia, and can be recommended as a personalized rehabilitation program for patients with poor effect of routine swallowing rehabilitation; ② fNIRS can be used as an objective neuroimaging tool to evaluate the therapeutic effect of taVNS and detect the reconstruction of the swallowing-related cortical network, which provides a basis for the individualized adjustment of taVNS parameters; ③ The key brain regions of taVNS’s effect (LPM, bilateral M1/S1) can be used as potential neuroimaging biomarkers for predicting the therapeutic effect of taVNS, and patients with low baseline activation of these brain regions may benefit more from taVNS intervention. 4.4 Study limitations and future perspectives This study has some limitations that need to be noted: ① The sample size is small and the study is a single-center trial, which may lead to insufficient statistical power and limit the external validity of the results. Future multi-center, large-sample randomized controlled trials are needed to verify the conclusions; ② The intervention period is short (2 weeks), and only the immediate effect of taVNS is observed. Long-term follow-up studies are needed to explore the long-term therapeutic effect and the persistence of cortical activation changes; ③ fNIRS can only detect the activation of the cerebral cortex, and cannot evaluate the changes of subcortical structures (e.g., thalamus, brainstem swallowing center) related to swallowing. Future studies can combine fNIRS with fMRI or EEG to conduct multi-modal neuroimaging research and comprehensively elucidate the neuromodulatory mechanism of taVNS; ④ Only one set of taVNS parameters and unilateral stimulation (left cymba conchae) are used in this study. Future studies can explore the therapeutic effects of different stimulation parameters (frequency, intensity, duration) and bilateral stimulation, and optimize the taVNS intervention protocol for post-stroke oral phase dysphagia. In the future, with the development of precision medicine and neuromodulation technology, the combination of taVNS and fNIRS will become a new direction for the rehabilitation of post-stroke dysphagia. Based on the fNIRS-detected cortical activation pattern, personalized taVNS intervention programs (e.g., parameter adjustment based on baseline cortical activation, targeted stimulation of key brain regions) can be formulated to further improve the therapeutic effect. In addition, the combination of taVNS with other neuromodulation therapies (e.g., rTMS, tDCS) and rehabilitation robots may produce a synergistic effect, which is worthy of further research. 5. Conclusion taVNS combined with routine swallowing rehabilitation is safe and effective for the treatment of post-stroke oral phase dysphagia, and has a superior effect on improving oral motor function compared with routine rehabilitation alone. The neurophysiological mechanism of taVNS is related to the enhancement of LPM activation (the key brain region regulating oral swallowing motor planning) and the promotion of extensive bilateral activation of M1 and S1, which optimizes the activation intensity and bilateral coordination pattern of the central swallowing motor-related cortical network, thereby facilitating the recovery of oral phase swallowing function. This study provides neurophysiological evidence for the clinical application of taVNS in post-stroke oral phase dysphagia, and lays a foundation for the development of personalized neuromodulation rehabilitation programs based on neuroimaging technology. Declarations Ethics approval and consent to participate This study was approved by The Second Affiliated Hospital of Dalian Medical University Ethics Committee (KY2025-105-01) in accordance with the declaration of Helsinki. All participants gave written informed consent prior to their enrollments. Consent for publication Not Applicable. Availability of data and materials The datasets generated and/or analysed during the current study are not publicly available due to ethical restrictions related to the protection of patient confidentiality (e.g., sensitive clinical and neurophysiological data of patients with neurogenic bladder). However, the de-identified individual participant data that underlie the results reported in this article will be made available upon reasonable request to the corresponding author ( [email protected] ) after approval from the Institutional Review Board of the Second Affiliated Hospital of Dalian Medical University. Competing interests The authors declare no competing interests. Funding Not applicable. Authors' contributions † These authors contributed equally to this work and share the first authorship. ‡Corresponding Author. Y D†: Conceptualization, Methodology, Investigation, Writing – original draft. J C†: Conceptualization, Methodology, Data curation, Formal analysis. M W: Investigation, Data collection, Validation, Writing – review & editing. D Z: Investigation, Data collection, Formal analysis. J P: Resources, Investigation, Validation. C W: Resources, Supervision, Writing – review & editing. Y W: Resources, Supervision, Formal analysis. L W‡: Conceptualization, Supervision, Funding acquisition, Project administration, Writing – review & editing, Final approval of the manuscript. All authors have read and agreed to the published version of the manuscript and confirm that the work has not been published elsewhere nor is it under consideration for publication in any other journal. Acknowledgments The authors would like to thank all the patients who participated in this study and the rehabilitation therapists and nurses of the Rehabilitation Medicine Department of the Second Affiliated Hospital of Dalian Medical University for their support in the study implementation and data collection. References Banda KJ, Chu H, Kang XL, et al. Prevalence of dysphagia and risk of pneumonia and mortality in acute stroke patients: a meta-analysis. BMC Geriatr. 2022;22(1):420. Ma X, Peng Y, Zhong L, et al. Hemodynamic signal changes during volitional swallowing in dysphagia patients with different unilateral hemispheric stroke and brainstem stroke: a near-infrared spectroscopy study. Brain Res Bull. 2024;210:110880. Lee JH, Kim HS, Yun DH, et al. The Relationship Between Tongue Pressure and Oral Dysphagia in Stroke Patients. Ann Rehabil Med. 2016;40(4):620–8. Wang J, Ma Y, Zhang H, et al. 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J Neurophysiol. 2020;123(3):927–35. Yao L, Ye Q, Liu Y, et al. Electroacupuncture improves swallowing function in a post-stroke dysphagia mouse model by activating the motor cortex inputs to the nucleus tractus solitarii through the parabrachial nuclei. Nat Commun. 2023;14(1):810. Thickbroom GW, Byrnes ML, Sacco P, et al. The role of the supplementary motor area in externally timed movement: the influence of predictability of movement timing. Brain Res. 2000;874(2):233–41. Bremmer F, Schlack A, Shah NJ, et al. Polymodal motion processing in posterior parietal and premotor cortex: a human fMRI study strongly implies equivalencies between humans and monkeys. Neuron. 2001;29(1):287–96. Holmes M, Aalto D, Cummine J. Opening the dialogue: A preliminary exploration of hair color, hair cleanliness, light, and motion effects on fNIRS signal quality. PLoS ONE. 2024;19(5):e0304356. Zhang F, Reid A, Schroeder A, et al. Controlling jaw-related motion artifacts in functional near-infrared spectroscopy. J Neurosci Methods. 2023;15(388):109810. Li SY, Xu K, Wang YX, et al. Task-specific cortical mechanisms of taVNS-paired task-oriented training for post-stroke upper extremity dysfunction under cognitive load: an fNIRS study. Front Hum Neurosci. 2025;19:1652612. Hess F, Foerch C, Keil F, et al. Association of lesion pattern and dysphagia in acute intracerebral hemorrhage. Stroke. 2021;52(9):2921–9. Cui S, Wang K, Wu S, et al. Electroacupuncture modulates the activity of the hippocampus-nucleus tractus solitarii-vagus nerve pathway to reduce myocardial ischemic injury. Neural Regen Res. 2018;13(9):1609–18. Irani F, Platek SM, Bunce S, et al. Functional near infrared spectroscopy (fNIRS): an emerging neuroimaging technology with important applications for the study of brain disorders. Clin Neuropsychol. 2007;21(1):9–37. Chinese Rehabilitation Medicine Association Swallowing Disorder Rehabilitation Professional Committee. Guidelines for Rehabilitation Management of Swallowing Disorders in China. (2023 Edition).Chin J Phys Med Rehabil, 2023,45(12): 1057–1072. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9073140","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":620766552,"identity":"8b9be7d2-7d60-4509-8075-b2d8f5b13a35","order_by":0,"name":"Yongli Dai","email":"","orcid":"","institution":"Rehabilitation Department of the Second Affiliated Hospital of Dalian Medical University, Dalian 116031, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Yongli","middleName":"","lastName":"Dai","suffix":""},{"id":620766555,"identity":"c8d9e305-dfa8-4c4c-9de1-597ee1e4de48","order_by":1,"name":"jialin Cao","email":"","orcid":"","institution":"Rehabilitation Department of the Second Affiliated Hospital of Dalian Medical University, Dalian 116031, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"jialin","middleName":"","lastName":"Cao","suffix":""},{"id":620766556,"identity":"7708855a-bc35-4614-a114-41028680c75e","order_by":2,"name":"Mengchun Wang","email":"","orcid":"","institution":"Rehabilitation Department of the Second Affiliated Hospital of Dalian Medical University, Dalian 116031, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Mengchun","middleName":"","lastName":"Wang","suffix":""},{"id":620766563,"identity":"ce4a2bd5-c1ee-48a3-9b14-007663d10dff","order_by":3,"name":"Dandan Zhang","email":"","orcid":"","institution":"College of Health-Preservation and Wellness, Dalian Medical University, Dalian 116044, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Dandan","middleName":"","lastName":"Zhang","suffix":""},{"id":620766564,"identity":"3f2f049c-11db-47e5-911d-a5280843e024","order_by":4,"name":"Juntao Pan","email":"","orcid":"","institution":"College of Health-Preservation and Wellness, Dalian Medical University, Dalian 116044, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Juntao","middleName":"","lastName":"Pan","suffix":""},{"id":620766566,"identity":"445b6a30-a5c1-455b-b0e2-22b4091be959","order_by":5,"name":"Chengbin Wang","email":"","orcid":"","institution":"Rehabilitation Department of the Second Affiliated Hospital of Dalian Medical University, Dalian 116031, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Chengbin","middleName":"","lastName":"Wang","suffix":""},{"id":620766567,"identity":"fee9e60f-7e55-448e-8b2b-b126d4f2d07a","order_by":6,"name":"Yanying Wu","email":"","orcid":"","institution":"Rehabilitation Department of the Second Affiliated Hospital of Dalian Medical University, Dalian 116031, Liaoning, China;","correspondingAuthor":false,"prefix":"","firstName":"Yanying","middleName":"","lastName":"Wu","suffix":""},{"id":620766569,"identity":"2a480742-0d02-4dc6-9dc9-a4386135a875","order_by":7,"name":"Litong Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3UlEQVRIiWNgGAWjYBACPmY4k7mB4YOBjR1BLWzMcD2MDYwzCtKSCWthQNLCzPPhEGMDQS3s/AcfF/w6LG/Ov7BN2sbgADMD++GjGwg4jNl4Zt9hw50zHrZJ5xjc4WPgSUu7QUALmzRvz23GDTcONhvnGDxjZpDgMSNKiz1Yi4XBYcYGorTw/LiduOF8Y+NjBiK1GBvzNvxP3nCDsfFhj0FaMhshv/DzH3z4mOdPmu2G84cPHPjxx8aOn/3wMbxawICxDUhIJEDtJagcDP6A7DtAnNpRMApGwSgYeQAAcsVImjFw4PgAAAAASUVORK5CYII=","orcid":"","institution":"Sports Medicine Center of the Second Affiliated Hospital of Dalian Medical University, Dalian 116023, Liaoning, China;","correspondingAuthor":true,"prefix":"","firstName":"Litong","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2026-03-09 12:53:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9073140/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9073140/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106965706,"identity":"4c4a362a-620d-4b47-9e18-38d1d1334bc3","added_by":"auto","created_at":"2026-04-15 09:56:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":173058,"visible":true,"origin":"","legend":"\u003cp\u003eFunctional near-infrared spectroscopy (fNIRS) channel distribution and corresponding cortical regions of interest (ROIs) based on the Brodmann atlas. Red circles represent light sources, blue squares represent detectors, and black intersections indicate 35 valid detection channels (source-detector distance: 3 cm). ROIs correspond to Brodmann areas: prefrontal cortex (PFC, BA9/10), premotor/supplementary motor cortex (PM, BA6), primary motor cortex (M1, BA4), and primary somatosensory cortex (S1, BA3/1/2). The probe cap was placed according to the international 10-20 system.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/f40ee1f7d69ad9aa80480bfb.png"},{"id":106962070,"identity":"e2974546-053e-4aa6-8081-a31cae40fe45","added_by":"auto","created_at":"2026-04-15 09:33:00","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":469134,"visible":true,"origin":"","legend":"\u003cp\u003eCortical activation intensity (oxyhemoglobin, HbO β-value) of each ROI in the chewing task before and after intervention in the two groups. Data are presented as Mean±SD. ROIs: LeftPFC (L-PFC), RightPFC (R-PFC), LeftPM (L-PM), RightPM (R-PM), LeftM1 (L-M1), RightM1 (R-M1), LeftS1 (L-S1), RightS1 (R-S1). *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, **\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01 vs. baseline (paired t-test). The taVNS group showed significantly stronger L-PM activation than the conventional group at post-intervention (**\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01, independent t-test). Pre-CT：Pre Conventional Therapy. Post-CT: Post Conventional Therapy. Pre-taVNS: Pre Transcutaneous auricular vagus nerve stimulation. Post-taVNS: Post Transcutaneous auricular vagus nerve stimulation.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/a264397d1b75d38bede484f7.png"},{"id":106962848,"identity":"e28dc5e4-204d-437d-8444-fb378f201300","added_by":"auto","created_at":"2026-04-15 09:40:15","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":199628,"visible":true,"origin":"","legend":"\u003cp\u003eIntragroup and intergroup comparison of ROI activation intensity (HbO β-value) in the chewing task. (A) Baseline comparison between the conventional Therapy group and taVNS group; (B) Intragroup comparison of the conventional Therapy group (baseline vs. post-intervention); (C) Intragroup comparison of the taVNS group (baseline vs. post-intervention); (D) Intergroup comparison of post-intervention activation intensity. Data are presented as Mean±SD. *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, **\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01 (paired t-test for intragroup comparison, independent t-test for intergroup comparison). Effect sizes (Cohen’s d) for key differences: taVNS group L-PM intragroup d=1.18, intergroup d=0.92 (large effect).\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/dfaeb445b6e4b8211141074a.png"},{"id":106962067,"identity":"8ff51688-f3a8-451e-bb17-e06ae729efd2","added_by":"auto","created_at":"2026-04-15 09:32:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":448006,"visible":true,"origin":"","legend":"\u003cp\u003eCortical activation intensity (HbO β-value) of each ROI in the tongue tip sliding task before and after intervention in the two groups. Data are presented as Mean±SD. ROIs are consistent with Fig. 2. *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, **\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01 vs. baseline (paired t-test). The taVNS group showed additional significant activation enhancement in RightM1 (RM1) and LeftS1 (LS1) (both *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05), which was not observed in the conventional Therapy group.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/f8d1be51c72e708a504596d6.png"},{"id":106962673,"identity":"13df3c49-6b2c-4f84-bc1f-40dca0d07bef","added_by":"auto","created_at":"2026-04-15 09:39:27","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":192365,"visible":true,"origin":"","legend":"\u003cp\u003eIntragroup and intergroup comparison of ROI activation intensity (HbO β-value) in the tongue tip sliding task. (A) Baseline comparison between groups; (B) Intragroup comparison of the conventional Therapy group; (C) Intragroup comparison of the taVNS group; (D) Intergroup comparison of post-intervention activation intensity. Data are presented as Mean±SD. *\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05, **\u003cem\u003ep\u003c/em\u003e\u0026lt;0.01 (paired t-test for intragroup comparison, independent t-test for intergroup comparison). The taVNS group’s unique activation in RM1 and LS1 is marked with red arrows (C panel).\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/49ef3d0fd376ac9c097ef321.png"},{"id":106962833,"identity":"65aaeff9-c596-4c2e-804a-6c68d1332a80","added_by":"auto","created_at":"2026-04-15 09:40:07","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":242973,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the neurophysiological mechanism of taVNS in improving post-stroke oral phase dysphagia:Transcutaneous auricular vagus nerve stimulation (taVNS) is applied to the left cymba conchae, activating the vagal afferent branch. Neural signals are relayed to the thalamus, which then modulates the excitability of swallowing-related cortical regions. Key effects include enhanced activation of the left premotor cortex (LPM) for motor planning, expanded bilateral activation of the primary motor (M1) and somatosensory (S1) cortices for sensory-motor integration, and regulation of the right prefrontal cortex (RPFC) to reduce psychological burden. These central changes collectively lead to improved oral motor function, enhanced swallowing-related quality of life (QOL), and reduced swallowing impairment, as measured by clinical scales (OFS, SWAL-QOL, SSA). The referenced figures and statistical results are consistent with the study’s core findings.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/83237af8eeadf1a196a770d9.png"},{"id":107338707,"identity":"115bb43d-a7db-4cfd-bc59-b50eaf81f2d2","added_by":"auto","created_at":"2026-04-20 13:57:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2453522,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9073140/v1/85bddb5c-c208-4c10-bb8c-799fa50c1817.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDysphagia is a common and debilitating complication after stroke, with a prevalence ranging from 50% to 80% in acute and recovery phases [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Among them, oral phase dysphagia accounts for approximately 40% of post-stroke dysphagia cases [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], characterized by impaired mastication, tongue movement dysfunction, and oral residue, which not only leads to malnutrition and dehydration but also increases the risk of aspiration pneumonia, significantly reducing patients\u0026rsquo; quality of life and increasing medical burdens [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The oral phase of swallowing is a complex voluntary motor process regulated by a network of cerebral cortical regions, including the primary motor/somatosensory cortex (M1/S1), premotor/supplementary motor cortex (PM), and prefrontal cortex (PFC) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Stroke-induced damage to this cortical network leads to abnormal neural activation and impaired neural plasticity, which is the core neurophysiological basis of oral phase dysphagia [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRoutine swallowing rehabilitation (e.g., sensory stimulation, motor training) is the first-line treatment for post-stroke dysphagia, which can improve peripheral swallowing muscle function through the \"peripheral-central\" feedback pathway [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, its effect on reversing central cortical network dysfunction is limited, and a considerable number of patients still have persistent swallowing impairment [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In recent years, non-invasive neuromodulation therapies have become a research hotspot for improving post-stroke neurological dysfunction by regulating cortical neural plasticity. Transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) have been applied in the treatment of post-stroke dysphagia [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], but their clinical application is restricted by high cost, strict operational requirements, and limited stimulation coverage. Transcutaneous auricular vagus nerve stimulation (taVNS), as a novel non-invasive neuromodulation technology, stimulates the auricular branch of the vagus nerve in the cymba conchae, which can ascend to activate the vagal afferent nucleus, thalamus, and multiple cerebral cortical regions [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. It has the advantages of simplicity, low cost, and wide cortical stimulation coverage, and has been proven to improve motor and cognitive function in stroke patients [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. A recent clinical study found that taVNS combined with routine rehabilitation can improve post-stroke dysphagia [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], but its specific effect on the oral phase and the underlying cortical activation mechanism remain unclear, which limits its personalized clinical application.\u003c/p\u003e \u003cp\u003eFunctional near-infrared spectroscopy (fNIRS) is a non-invasive neuroimaging technology that reflects cortical neural activity by detecting changes in oxyhemoglobin (HbO) concentration based on the neurovascular coupling mechanism [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Compared with functional magnetic resonance imaging (fMRI) and electroencephalography (EEG), fNIRS has the advantages of high portability, low motion artifact sensitivity, and compatibility with clinical motor tasks [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], making it an ideal tool for real-time detection of cortical activation during swallowing motor tasks. In recent years, fNIRS has been widely used to explore the cortical mechanism of swallowing and the therapeutic effect of neuromodulation therapies [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Previous fNIRS studies have confirmed that M1, S1, PM, and PFC are the core brain regions regulating the oral phase swallowing tasks (e.g., mastication, tongue movement) [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], and the recovery of post-stroke dysphagia is closely related to the reconstruction of the activation pattern of these brain regions [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, there are few studies on the changes in cortical activation of taVNS for post-stroke oral phase dysphagia detected by fNIRS.\u003c/p\u003e \u003cp\u003e This study adopted a randomized controlled design to compare the effects of taVNS combined with routine swallowing rehabilitation and sham taVNS combined with routine rehabilitation on the swallowing function of patients with post-stroke oral phase dysphagia. fNIRS was used to detect the cortical activation changes of the core swallowing-related brain regions (PFC, PM, M1, S1) during two typical oral phase swallowing tasks (chewing and tongue tip sliding). We hypothesized that taVNS could enhance the activation of swallowing-related cortical regions and optimize the bilateral activation pattern, thereby improving oral phase swallowing function. The results of this study will provide neurophysiological evidence for the clinical application of taVNS in post-stroke oral phase dysphagia and lay a foundation for the development of personalized neuromodulation rehabilitation programs.\u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Study design and participants\u003c/h2\u003e \u003cp\u003e This was a single-blind, randomized controlled trial approved by the Ethics Committee of the Second Affiliated Hospital of Dalian Medical University (KY2025-105-01) and conducted in accordance with the Declaration of Helsinki. A total of 40 patients with post-stroke oral phase dysphagia were recruited from the Rehabilitation Medicine Department of our hospital from July 2023 to January 2025.\u003c/p\u003e \u003cp\u003e \u003cb\u003eInclusion criteria\u003c/b\u003e: ① Met the diagnostic criteria for cerebral hemorrhage or cerebral infarction formulated by the Fourth National Cerebrovascular Disease Academic Conference of the Chinese Medical Association [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and confirmed by cranial computed tomography (CT) or magnetic resonance imaging (MRI); ② Unilateral lesion, first onset, and onset time of 7 days to 1 month; ③ Grade 2\u0026ndash;5 on the Water Swallowing Test(WST), with typical clinical manifestations of oral phase dysphagia (e.g., impaired mastication, tongue movement disorder); ④ Aged 30\u0026ndash;70 years; ⑤ No obvious cognitive impairment (Mini-Mental State Examination, MMSE: illiterate\u0026thinsp;\u0026gt;\u0026thinsp;17 points, primary school\u0026thinsp;\u0026gt;\u0026thinsp;20 points, junior high school and above \u0026gt;\u0026thinsp;24 points); ⑥ Signed informed consent voluntarily.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eExclusion criteria\u003c/strong\u003e \u003cp\u003e① Skull defect; ② Tracheostomy status; ③ Ineligible for auricular electrical stimulation (e.g., auricular infection, ulcer, scar); ④ Resting heart rate\u0026thinsp;\u0026lt;\u0026thinsp;60 beats/min; ⑤ Implanted medical devices such as cardiac pacemaker and cochlear implant; ⑥ A history of vagus nerve surgery; ⑦ A history of oral and maxillofacial surgery or structural dysfunction of the oral and maxillofacial region; ⑧ Other neurological or muscular diseases interfering with assessment (e.g., oral fibrosis, masticatory muscle atrophy).\u003c/p\u003e \u003c/p\u003e \u003cp\u003ePatients were randomly assigned to the conventional Therapy group and the taVNS group at a 1:1 ratio using the lottery method. The evaluators of swallowing function and fNIRS data analysts were blinded to the group assignment, and the patients were unaware of the type of stimulation (real/sham).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Interventional protocols\u003c/h2\u003e \u003cp\u003eBoth groups received 2 weeks of routine swallowing rehabilitation (5 sessions/week, 1 session/day, 30 min/session), and the taVNS intervention (real/sham) was performed 30 minutes before each rehabilitation session, with a duration of 25 min/session.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Routine swallowing rehabilitation\u003c/h2\u003e \u003cp\u003e The rehabilitation program was formulated by professional rehabilitation therapists and included the following components: ① Acid stimulation: Diluted acidic liquids (lemon juice/vinegar) were used to stimulate the tongue and oral mucosa; ② Ice stimulation: Ice cubes were used to gently stimulate the pharynx, neck, and tongue body; ③ Vibration sensory stimulation: A vibration rod was used for mild vibration stimulation of the pharynx and jaw; ④ Pharyngeal swallowing muscle massage: Manual massage of the pharyngeal and laryngeal muscles; ⑤ Swallowing motor training: Facial muscle training (pursed lips, teeth showing, cheek puffing) and tongue muscle resistance training (tongue retractor traction of the anterior tongue).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 taVNS intervention\u003c/h2\u003e \u003cp\u003eA low-frequency pulsed electrical stimulator (En-stim4, Shanghai Xibei Electronic Technology Development Co., Ltd., China) with biphasic pulsed current mode was used for both real and sham taVNS. The stimulation parameters were consistent: pulse frequency 25 Hz, pulse width 0.5 ms, 30 s stimulation with 30 s interval, and the current intensity was adjusted to 0.1 mA below the pain threshold.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003etaVNS group (real stimulation)\u003c/b\u003e: The left cymba conchae (the innervation area of the auricular branch of the vagus nerve) was routinely disinfected, and the electrodes were placed on the left cymba conchae for electrical stimulation.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eConventional Therapy group (sham stimulation)\u003c/b\u003e: The left earlobe (non-innervation area of the auricular branch of the vagus nerve) was routinely disinfected, and the electrodes were placed on the left earlobe for electrical stimulation with the same parameters as the taVNS group.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Outcome assessments\u003c/h2\u003e \u003cp\u003eAll assessments were completed by the same trained rehabilitation evaluator before intervention (baseline) and immediately after 2 weeks of intervention. The assessment indicators included swallowing function scales and fNIRS cortical activation detection, and safety assessment was performed during the entire intervention period.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Swallowing function scale assessment\u003c/h2\u003e \u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eStandardized Swallowing Assessment (SSA)\u003c/b\u003e: A reliable and valid scale for evaluating swallowing function, including clinical examination (8\u0026ndash;23 points), 5 ml warm water swallowing test (5\u0026ndash;11 points), and 60 ml warm water swallowing test (5\u0026ndash;12 points), with a total score of 18\u0026ndash;46 points. A higher score indicates worse swallowing function [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eOral Function Scale (OFS)\u003c/b\u003e: A scale for evaluating oral motor function in dysphagia patients, including 7 items such as mastication, swallowing, and tongue flexibility. Each item is scored as 1 (unable to perform), 2 (needing assistance/modification), and 3 (able to perform independently), with a total score ranging from 7 to 21 points. A higher score indicates better oral function [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eSwallowing-Quality of Life (SWAL-QOL)\u003c/b\u003e: A specific scale for evaluating the quality of life of dysphagia patients, including 44 items covering 11 dimensions (8 swallowing-related dimensions: psychological burden, eating time, appetite, food choice, verbal communication, fear of eating, mental health, social interaction; 2 general dimensions: fatigue, sleep; 1 dysphagia frequency dimension). Each item is scored on a 5-point Likert scale (1\u0026ndash;5 points), with a higher total score indicating a better quality of life related to swallowing [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 fNIRS detection\u003c/h2\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003efNIRS device and probe placement\u003c/b\u003e: A 35-channel fNIRS system (Huichuang Medical Equipment Co., Ltd., Danyang, China) with two near-infrared wavelengths (730 nm and 850 nm) was used to detect the changes in HbO and deoxyhemoglobin (HbR) concentrations in the cerebral cortex. The probe cap included 14 light sources and 14 detectors, with a probe spacing of approximately 3 cm, forming 35 detection channels. The probe cap was placed according to the international 10\u0026ndash;20 system, and the target regions of interest (ROIs) included the left/right PFC, left/right PM, left/right M1, and left/right S1. The channel positions corresponding to each ROI were determined based on the Brodmann atlas (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eTask paradigm\u003c/b\u003e: All patients completed two oral phase swallowing motor tasks in a quiet and comfortable environment: \u003cb\u003echewing task\u003c/b\u003e (simulating mastication at a daily eating frequency) and \u003cb\u003etongue tip sliding task\u003c/b\u003e (sliding the tongue tip along the hard palate backward at a voluntary rhythm). Each task adopted a block design: 3 rest blocks and 3 task blocks, with each block lasting 30 s. A 30 s resting state data was collected before the start of the task and after each task block (patients kept relaxed, sitting still, and avoiding thinking). The total duration of each task was 210 s, and a 1-minute rest was given between the two tasks to avoid fatigue.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003efNIRS data processing\u003c/b\u003e: fNIRS data was processed using the NIRS-KIT toolbox based on MATLAB R2021a (MathWorks, USA), following the standard processing pipeline [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]: ① Converting raw light intensity data into HbO and HbR concentrations based on the Beer-Lambert law; ② Previewing and removing obvious bad channels; ③ Eliminating linear drift using a polynomial regression model; ④ Correcting motion artifacts using the temporal derivative distribution repair method; ⑤ Band-pass filtering (0.01\u0026ndash;0.08 Hz) using a third-order Butterworth filter. Considering the higher signal-to-noise ratio of HbO compared with HbR [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], only HbO data was used for subsequent cortical activation analysis.\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003e\u003cb\u003eCortical activation quantification\u003c/b\u003e: A general linear model (GLM) based on the hemodynamic response function (HRF) was used to model the task-related hemodynamic activity of each channel at the individual level, and the β value (regression coefficient) of each channel was calculated to reflect the cortical activation intensity. The average β value of all channels in each ROI was taken as the activation intensity of the corresponding brain region [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3 Safety assessment\u003c/h2\u003e \u003cp\u003eBlood pressure, pulse, and heart rate of patients were measured using a sphygmomanometer and stethoscope before and after each taVNS (real/sham) intervention to evaluate the risk of cardiac adverse reactions. After each intervention, patients were asked about subjective discomfort (e.g., auricular pain, burning sensation, dizziness), and the occurrence of adverse events was recorded in detail.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll data were collated using Microsoft Excel 2021 and statistically analyzed using SPSS 27.0 (IBM, USA) and G*Power 3.1. Measurement data were expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) after verifying normality via the Shapiro-Wilk test and homogeneity of variance via Levene\u0026rsquo;s test.\u003c/p\u003e \u003cp\u003eSample size calculation was performed a priori based on the primary outcome (Oral Function Scale [OFS] score): assuming an effect size \u003cem\u003ef\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.25, significance level \u003cem\u003eα\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.05, and statistical power 1\u0026thinsp;\u0026minus;\u0026thinsp;\u003cem\u003eβ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.80, the calculation indicated that 34 participants (17 per group) were required to detect significant between-group differences. Considering a potential 20% dropout rate, 40 participants (20 per group) were enrolled, ensuring sufficient statistical power for core outcomes.\u003c/p\u003e \u003cp\u003eIntragroup comparisons of baseline and post-intervention data were performed using paired samples \u003cem\u003et\u003c/em\u003e-test, and intergroup comparisons of post-intervention data were conducted using independent samples \u003cem\u003et\u003c/em\u003e-test. Repeated-measures analysis of variance (RM-ANOVA) was further used to confirm the interaction effect of \"group \u0026times; time\" (with age and stroke type as covariates), The interaction effect of 'group \u0026times; time' was significant for OFS score (F\u0026thinsp;=\u0026thinsp;4.89, p\u0026thinsp;=\u0026thinsp;0.032) and LPM activation (F\u0026thinsp;=\u0026thinsp;5.12, p\u0026thinsp;=\u0026thinsp;0.028), confirming that the therapeutic effect of taVNS was independent of age and stroke type,and the results were consistent with \u003cem\u003et\u003c/em\u003e-test findings (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Effect sizes (Cohen\u0026rsquo;s d) were calculated to quantify the magnitude of differences: d\u0026thinsp;\u0026gt;\u0026thinsp;0.8 was considered a large effect, 0.5\u0026ndash;0.8 a medium effect, and 0.2\u0026ndash;0.5 a small effect.\u003c/p\u003e \u003cp\u003eCount data were expressed as percentage (%), and comparisons were performed using the chi-square test. \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Baseline clinical characteristics\u003c/h2\u003e \u003cp\u003eA total of 40 patients were enrolled in the study, with 20 patients in each group, and all completed the intervention and assessments (no dropout). There were no significant differences in baseline clinical characteristics (age, gender, stroke type, affected hemisphere) and swallowing function scores (SSA, OFS, SWAL-QOL) between the two groups (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), indicating good group balance (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of baseline clinical characteristics between the two groups (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eConventional Therapy group (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003etaVNS group (n\u0026thinsp;=\u0026thinsp;20)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e/χ\u0026sup2; value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAge (years)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58.67\u0026thinsp;\u0026plusmn;\u0026thinsp;8.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56.79\u0026thinsp;\u0026plusmn;\u0026thinsp;8.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.702\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.483\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGender (male:female, n)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14:6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13:7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.743\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStroke type (ischemic:hemorrhagic, n)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e13:7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15:5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.457\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.502\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAffected hemisphere (left:right, n)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12:8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11:9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.756\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStandardized Swallowing Assessment (SSA) total score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23.33\u0026thinsp;\u0026plusmn;\u0026thinsp;1.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.23\u0026thinsp;\u0026plusmn;\u0026thinsp;2.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.905\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOral Function Scale (OFS) total score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.157\u0026thinsp;\u0026plusmn;\u0026thinsp;2.627\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.861\u0026thinsp;\u0026plusmn;\u0026thinsp;2.877\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.320\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.444\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSwallowing-Quality of Life (SWAL-QOL) total score\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e121.42\u0026thinsp;\u0026plusmn;\u0026thinsp;4.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e119.31\u0026thinsp;\u0026plusmn;\u0026thinsp;8.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.901\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.361\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003eNote: Data are presented as Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD. Continuous variables were compared using independent samples t-test, and categorical variables using chi-square test. No significant differences were observed between groups at baseline (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Changes in swallowing function scale scores\u003c/h2\u003e \u003cp\u003eAfter 2 weeks of intervention, the swallowing function scores of the two groups showed different degrees of improvement, and the intragroup and intergroup comparison results were as follows (Tables\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSSA score\u003c/b\u003e: Both groups had significantly lower SSA scores after intervention compared with baseline (conventional group: \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.983, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.007; taVNS group: \u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.978, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.007), with no significant intergroup difference in post-intervention SSA score (\u003cem\u003et\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.852, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.403).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eOFS score\u003c/b\u003e: Both groups had significantly higher OFS scores after intervention compared with baseline (conventional group: \u003cem\u003et\u003c/em\u003e=-3.478, \u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001; taVNS group: \u003cem\u003et\u003c/em\u003e=-3.038, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.004). The post-intervention OFS score of the taVNS group was significantly higher than that of the conventional group (\u003cem\u003et\u003c/em\u003e=-3.451, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003e \u003cb\u003eSWAL-QOL score\u003c/b\u003e: The taVNS group had a significantly higher SWAL-QOL score after intervention compared with baseline (\u003cem\u003et\u003c/em\u003e=-3.029, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.006), while the conventional group had no significant change (\u003cem\u003et\u003c/em\u003e=-1.152, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.262). There was no significant intergroup difference in post-intervention SWAL-QOL score (\u003cem\u003et\u003c/em\u003e=-1.487, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.151).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Standardized Swallowing Assessment (SSA) total scores between the two groups before and after intervention (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePost-intervention\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eEffect size(Cohen\u0026rsquo;s d)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConventional Therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.333\u0026thinsp;\u0026plusmn;\u0026thinsp;1.723\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e21.333\u0026thinsp;\u0026plusmn;\u0026thinsp;1.557\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.983\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etaVNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23.231\u0026thinsp;\u0026plusmn;\u0026thinsp;2.421\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.769\u0026thinsp;\u0026plusmn;\u0026thinsp;1.739\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.978\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.121\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.852\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.905\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.403\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eNote: SSA total score ranges from 18 to 46, with higher scores indicating worse swallowing function. Intragroup comparisons were performed using paired samples t-test. Both groups showed significant improvement after intervention (both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), with no significant intergroup difference (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Cohen\u0026rsquo;s d\u0026thinsp;\u0026gt;\u0026thinsp;0.8 indicates a large effect size, 0.5\u0026ndash;0.8 a medium effect, and 0.2\u0026ndash;0.5 a small effect.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Oral Function Scale (OFS) total scores between the two groups before and after intervention (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePost-intervention\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eEffect size(Cohen\u0026rsquo;s d)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConventional Therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.712\u0026thinsp;\u0026plusmn;\u0026thinsp;1.456\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.312\u0026thinsp;\u0026plusmn;\u0026thinsp;1.454\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.478\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etaVNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.561\u0026thinsp;\u0026plusmn;\u0026thinsp;2.877\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8.231\u0026thinsp;\u0026plusmn;\u0026thinsp;1.684\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.038\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.004\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.581\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-3.451\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.561\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eNote: OFS total score ranges from 7 to 21, with higher scores indicating better oral motor function. Intragroup comparisons were performed using paired samples t-test, and intergroup comparison using independent samples t-test. Both groups showed significant improvement after intervention (both \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01), and the taVNS group had a significantly higher score than the conventional group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) with a large effect size (d\u0026thinsp;=\u0026thinsp;1.35).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Swallowing-Quality of Life (SWAL-QOL) total scores between the two groups before and after intervention (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003en\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBaseline\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePost-intervention\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eEffect size(Cohen\u0026rsquo;s d)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eConventional Therapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e121.417\u0026thinsp;\u0026plusmn;\u0026thinsp;4.944\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e124.167\u0026thinsp;\u0026plusmn;\u0026thinsp;6.631\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.152\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.262\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003etaVNS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e119.308\u0026thinsp;\u0026plusmn;\u0026thinsp;8.077\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e128.154\u0026thinsp;\u0026plusmn;\u0026thinsp;6.756\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003et\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.779\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.487\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eP\u003c/em\u003e value (intergroup)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.444\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.151\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"7\"\u003eNote: SWAL-QOL total score ranges from 32 to 160, with higher scores indicating better swallowing-related quality of life. Intragroup comparisons were performed using paired samples t-test. Only the taVNS group showed significant improvement after intervention (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.01) with a large effect size (d\u0026thinsp;=\u0026thinsp;1.21), while the conventional group had no significant change (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Changes in fNIRS cortical activation\u003c/h2\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.3.1 Chewing task\u003c/h2\u003e \u003cp\u003eAt baseline, there was no significant difference in the activation intensity of all ROIs between the two groups (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After intervention, both groups showed significant activation enhancement in RPFC, LPM, and LM1 compared with baseline (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Intergroup comparison of post-intervention activation intensity showed that the taVNS group had significantly stronger LPM activation than the conventional group (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD: 0.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16 vs. 0.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14, p\u0026thinsp;\u0026lt;\u0026thinsp;0.05, Cohen\u0026rsquo;s d\u0026thinsp;=\u0026thinsp;0.92), with no significant differences in RPFC and LM1 (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e \u003ch2\u003e3.3.2 Tongue tip sliding task\u003c/h2\u003e \u003cp\u003eAt baseline, there was no significant difference in the activation intensity of all ROIs between the two groups (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After intervention, both groups exhibited significant activation enhancement in LPM, RPM, LM1, and RS1 compared with baseline (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In addition, the taVNS group had significant activation increases in RM1 and LS1 after intervention (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), which was not observed in the conventional group (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Intergroup comparison of post-intervention activation intensity showed no significant differences in all ROIs between the two groups (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), but the taVNS group exhibited a more extensive bilateral activation pattern characterized by additional activation of RM1 and LS1 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Safety assessment\u003c/h2\u003e \u003cp\u003eNo severe adverse events (e.g., cardiac arrhythmia, severe hypotension, dizziness) were observed in either group during the 2-week intervention. Only 1 patient in the taVNS group reported a mild burning sensation in the left cymba conchae during the first intervention, and the discomfort disappeared after suspending the intervention, cleaning the auricular skin, and appropriately reducing the current intensity. No other subjective discomfort was reported by the patients, and the tolerance of the intervention was good.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e This study confirmed that taVNS combined with routine swallowing rehabilitation can safely and effectively improve the oral phase swallowing function of stroke patients, and has a superior effect on enhancing oral motor function compared with routine rehabilitation alone. For the first time, fNIRS was used to clarify the neurophysiological mechanism of taVNS in improving oral phase dysphagia: taVNS can enhance the activation of LPM (a key brain region regulating oral swallowing) and promote extensive bilateral activation of M1 and S1, thereby optimizing the activation pattern of the central swallowing motor cortical network.\u003c/p\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.1 taVNS improves oral phase swallowing function: clinical efficacy analysis\u003c/h2\u003e \u003cp\u003eRoutine swallowing rehabilitation can improve the oral phase swallowing function of stroke patients by stimulating peripheral sensory receptors and training swallowing muscles, which is consistent with the significant improvement of SSA and OFS scores in the conventional group in this study [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. However, the conventional group had no significant improvement in SWAL-QOL scores, suggesting that routine rehabilitation only improves objective swallowing motor function, and has a limited effect on patients\u0026rsquo; subjective quality of life related to swallowing (e.g., psychological burden, fear of eating). The taVNS group had significant improvements in SSA, OFS, and SWAL-QOL scores, and the OFS score was significantly higher than that of the conventional group, indicating that taVNS can produce an additional therapeutic effect on the basis of routine rehabilitation, especially in improving oral motor function, and also has a positive effect on improving patients\u0026rsquo; subjective swallowing quality of life.\u003c/p\u003e \u003cp\u003e The superior effect of taVNS on oral motor function may be related to its specific regulation of the oral swallowing motor network. The oral phase of swallowing is a voluntary motor process dominated by the cortical motor system, and PM, M1, and S1 are the core brain regions regulating oral motor functions such as mastication and tongue movement [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. taVNS can activate the vagal afferent pathway to regulate the excitability of the cortical motor system [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], thereby enhancing the neural control of oral swallowing muscles and improving oral motor function (e.g., tongue flexibility, mastication ability), which is reflected in the significant improvement of OFS scores. In addition, taVNS has been proven to regulate the activity of the prefrontal cortex and improve the negative emotions of stroke patients [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The RPFC activation was significantly enhanced in the taVNS group in this study, which may reduce the psychological burden and fear of eating of patients with dysphagia, thus improving the SWAL-QOL score.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Neurophysiological mechanism of taVNS: analysis of cortical activation changes\u003c/h2\u003e \u003cdiv id=\"Sec22\" class=\"Section3\"\u003e \u003ch2\u003e4.2.1 Chewing task: enhanced LPM activation is the core of taVNS\u0026rsquo;s effect\u003c/h2\u003e \u003cp\u003eChewing is a typical oral phase swallowing task, which mainly involves the cognitive preparation, motor planning, and executive control of swallowing [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The results of this study showed that both groups had significant activation enhancement in RPFC, LPM, and LM1 after intervention, indicating that routine rehabilitation can also promote the reconstruction of the cortical network related to chewing, which is consistent with previous fNIRS studies [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. The key finding of this study is that the taVNS group had significantly stronger LPM activation than the conventional group after intervention, suggesting that enhanced LPM activation is the core neurophysiological basis of taVNS\u0026rsquo;s additional therapeutic effect.\u003c/p\u003e \u003cp\u003ePM is an important brain region connecting the cognitive control and motor execution of swallowing, which receives sensory input from the parietal cortex, integrates motor information, and projects to M1 and spinal motor neurons to regulate the coordination of swallowing muscles [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. For stroke patients with unilateral lesion, the damage of the swallowing motor network leads to the decline of PM activation and the loss of motor planning ability, which is an important reason for impaired mastication and uncoordinated tongue movement [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. taVNS can increase the release of neurotransmitters (e.g., glutamate, gamma-aminobutyric acid) in the cerebral cortex by activating the vagal afferent pathway, enhance the neural plasticity of the cortical motor system [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and thus significantly improve the activation intensity of LPM. The enhanced LPM activation can optimize the motor planning of oral swallowing, improve the coordination of masticatory and tongue muscles, and ultimately lead to the significant improvement of oral motor function, which is consistent with the higher OFS score in the taVNS group.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003e4.2.2 Tongue tip sliding task: taVNS promotes extensive bilateral activation of M1 and S1\u003c/h2\u003e \u003cp\u003eTongue tip sliding is a key task in the transition from the oral phase to the pharyngeal phase of swallowing, which requires the close cooperation of oral sensory and motor functions, and the bilateral coordination of M1 and S1 is crucial for the smooth completion of this task [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The results of this study showed that both groups had significant activation enhancement in LPM, RPM, LM1, and RS1 after intervention, indicating that routine rehabilitation can promote the activation of the bilateral PM and the sensorimotor cortex related to tongue movement. Notably, the taVNS group also had significant activation increases in RM1 and LS1 after intervention, showing a more extensive bilateral activation pattern of M1 and S1, which is another important neurophysiological mechanism of taVNS\u0026rsquo;s effect.\u003c/p\u003e \u003cp\u003ePost-stroke brain damage leads to the imbalance of the bilateral sensorimotor cortex and the loss of bilateral coordination, which is the main reason for the disorder of tongue movement and the difficulty in the transition from oral to pharyngeal phase [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. A previous fNIRS study confirmed that the recovery of post-stroke dysphagia is closely related to the reconstruction of the bilateral activation pattern of the swallowing-related sensorimotor cortex [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. taVNS has a wide range of cortical stimulation effects, which can not only activate the affected side cortex but also regulate the excitability of the unaffected side cortex [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], thereby promoting the reconstruction of the bilateral balance of the sensorimotor cortex. The extensive bilateral activation of M1 and S1 in the taVNS group can enhance the sensory and motor integration of tongue movement, improve the flexibility and coordination of the tongue, and facilitate the smooth transition from the oral phase to the pharyngeal phase of swallowing. Although there was no significant intergroup difference in the activation intensity of all brain regions in the tongue tip sliding task, the more extensive bilateral activation pattern in the taVNS group is an important neurophysiological basis for its long-term therapeutic effect, which needs to be verified by follow-up studies with a longer intervention period.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Safety and clinical implications of taVNS\u003c/h2\u003e \u003cp\u003eIn this study, taVNS had good safety and tolerance, with only one case of mild auricular burning sensation, which was relieved after simple intervention. No cardiac or neurological adverse events were observed, which is consistent with previous clinical studies on taVNS [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The selection of the left cymba conchae as the stimulation site is the key to ensuring safety, because the left vagus nerve has a weaker cardiac vagal effect, which can avoid the risk of bradycardia and hypotension [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The stimulation parameters (25 Hz, 0.5 ms pulse width) used in this study are conventional clinical parameters, which have been proven to be safe and effective in previous taVNS studies for stroke [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], and can be directly applied to clinical practice.\u003c/p\u003e \u003cp\u003e The clinical implications of this study are significant: ① taVNS is a safe and effective adjuvant therapy for post-stroke oral phase dysphagia, and can be recommended as a personalized rehabilitation program for patients with poor effect of routine swallowing rehabilitation; ② fNIRS can be used as an objective neuroimaging tool to evaluate the therapeutic effect of taVNS and detect the reconstruction of the swallowing-related cortical network, which provides a basis for the individualized adjustment of taVNS parameters; ③ The key brain regions of taVNS\u0026rsquo;s effect (LPM, bilateral M1/S1) can be used as potential neuroimaging biomarkers for predicting the therapeutic effect of taVNS, and patients with low baseline activation of these brain regions may benefit more from taVNS intervention.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Study limitations and future perspectives\u003c/h2\u003e \u003cp\u003eThis study has some limitations that need to be noted: ① The sample size is small and the study is a single-center trial, which may lead to insufficient statistical power and limit the external validity of the results. Future multi-center, large-sample randomized controlled trials are needed to verify the conclusions; ② The intervention period is short (2 weeks), and only the immediate effect of taVNS is observed. Long-term follow-up studies are needed to explore the long-term therapeutic effect and the persistence of cortical activation changes; ③ fNIRS can only detect the activation of the cerebral cortex, and cannot evaluate the changes of subcortical structures (e.g., thalamus, brainstem swallowing center) related to swallowing. Future studies can combine fNIRS with fMRI or EEG to conduct multi-modal neuroimaging research and comprehensively elucidate the neuromodulatory mechanism of taVNS; ④ Only one set of taVNS parameters and unilateral stimulation (left cymba conchae) are used in this study. Future studies can explore the therapeutic effects of different stimulation parameters (frequency, intensity, duration) and bilateral stimulation, and optimize the taVNS intervention protocol for post-stroke oral phase dysphagia.\u003c/p\u003e \u003cp\u003eIn the future, with the development of precision medicine and neuromodulation technology, the combination of taVNS and fNIRS will become a new direction for the rehabilitation of post-stroke dysphagia. Based on the fNIRS-detected cortical activation pattern, personalized taVNS intervention programs (e.g., parameter adjustment based on baseline cortical activation, targeted stimulation of key brain regions) can be formulated to further improve the therapeutic effect. In addition, the combination of taVNS with other neuromodulation therapies (e.g., rTMS, tDCS) and rehabilitation robots may produce a synergistic effect, which is worthy of further research.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003e taVNS combined with routine swallowing rehabilitation is safe and effective for the treatment of post-stroke oral phase dysphagia, and has a superior effect on improving oral motor function compared with routine rehabilitation alone. The neurophysiological mechanism of taVNS is related to the enhancement of LPM activation (the key brain region regulating oral swallowing motor planning) and the promotion of extensive bilateral activation of M1 and S1, which optimizes the activation intensity and bilateral coordination pattern of the central swallowing motor-related cortical network, thereby facilitating the recovery of oral phase swallowing function. This study provides neurophysiological evidence for the clinical application of taVNS in post-stroke oral phase dysphagia, and lays a foundation for the development of personalized neuromodulation rehabilitation programs based on neuroimaging technology.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by The Second Affiliated Hospital of Dalian Medical University Ethics Committee (KY2025-105-01) in accordance with the declaration of Helsinki. All participants gave written informed consent prior to their enrollments.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot Applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analysed during the current study are not publicly available due to ethical restrictions related to the protection of patient confidentiality (e.g., sensitive clinical and neurophysiological data of patients with neurogenic bladder). However, the de-identified individual participant data that underlie the results reported in this article will be made available upon reasonable request to the corresponding author ([email protected]) after approval from the Institutional Review Board of the Second Affiliated Hospital of Dalian Medical University.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026dagger; These authors contributed equally to this work and share the first authorship.\u003c/p\u003e\n\u003cp\u003e\u0026Dagger;Corresponding Author.\u003c/p\u003e\n\u003cp\u003eY D\u0026dagger;: Conceptualization, Methodology, Investigation, Writing \u0026ndash; original draft.\u003c/p\u003e\n\u003cp\u003eJ C\u0026dagger;: Conceptualization, Methodology, Data curation, Formal analysis.\u003c/p\u003e\n\u003cp\u003eM W: Investigation, Data collection, Validation, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003eD Z: Investigation, Data collection, Formal analysis.\u003c/p\u003e\n\u003cp\u003eJ P: Resources, Investigation, Validation.\u003c/p\u003e\n\u003cp\u003eC W: Resources, Supervision, Writing \u0026ndash; review \u0026amp; editing.\u003c/p\u003e\n\u003cp\u003eY W: Resources, Supervision, Formal analysis.\u003c/p\u003e\n\u003cp\u003eL W\u0026Dagger;: Conceptualization, Supervision, Funding acquisition, Project administration, Writing \u0026ndash; review \u0026amp; editing, Final approval of the manuscript.\u003c/p\u003e\n\u003cp\u003eAll authors have read and agreed to the published version of the manuscript and confirm that the work has not been published elsewhere nor is it under consideration for publication in any other journal.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank all the patients who participated in this study and the rehabilitation therapists and nurses of the Rehabilitation Medicine Department of the Second Affiliated Hospital of Dalian Medical University for their support in the study implementation and data collection.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBanda KJ, Chu H, Kang XL, et al. 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Neural Regen Res. 2018;13(9):1609\u0026ndash;18.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIrani F, Platek SM, Bunce S, et al. Functional near infrared spectroscopy (fNIRS): an emerging neuroimaging technology with important applications for the study of brain disorders. Clin Neuropsychol. 2007;21(1):9\u0026ndash;37.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChinese Rehabilitation Medicine Association Swallowing Disorder Rehabilitation Professional Committee. Guidelines for Rehabilitation Management of Swallowing Disorders in China. (2023 Edition).Chin J Phys Med Rehabil, 2023,45(12): 1057\u0026ndash;1072.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Stroke, Oral phase dysphagia, Transcutaneous auricular vagus nerve stimulation, Functional near-infrared spectroscopy, Cortical activation, Neuromodulation","lastPublishedDoi":"10.21203/rs.3.rs-9073140/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9073140/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eTranscutaneous auricular vagus nerve stimulation (taVNS) is a promising non-invasive neuromodulation therapy for post-stroke neurological dysfunction, but its neurophysiological mechanism in improving oral phase dysphagia remains unclear. This study aimed to investigate the effects of taVNS combined with routine swallowing rehabilitation on swallowing function and cortical activation patterns in patients with post-stroke oral phase dysphagia using functional near-infrared spectroscopy (fNIRS), and to elucidate the potential neuromodulatory mechanism of taVNS.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA single-blind, randomized controlled trial was conducted on 40 patients with post-stroke oral phase dysphagia admitted to our hospital from July 2023 to January 2025. Patients were randomly assigned to the conventional Therapy group (n\u0026thinsp;=\u0026thinsp;20, sham taVNS\u0026thinsp;+\u0026thinsp;routine swallowing rehabilitation) and the taVNS group (n\u0026thinsp;=\u0026thinsp;20, real taVNS\u0026thinsp;+\u0026thinsp;routine swallowing rehabilitation) at a 1:1 ratio via lottery. The intervention lasted for 2 weeks (5 sessions/week, 30 min/session for rehabilitation, 25 min/session for taVNS). Swallowing function was assessed using the Standardized Swallowing Assessment (SSA), Oral Function Scale (OFS), and Swallowing-Quality of Life (SWAL-QOL) scale before and after intervention by the same blinded evaluator. fNIRS was used to detect cortical hemodynamic responses (oxyhemoglobin, HbO) during chewing and tongue tip sliding tasks, and the activation levels of the prefrontal cortex (PFC), premotor/supplementary motor cortex (PM), primary motor cortex (M1), and primary somatosensory cortex (S1) were quantified. NIRS-KIT and SPSS 27.0 were used for fNIRS data processing and statistical analysis, respectively.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThere were no significant differences in baseline clinical characteristics and swallowing function scores between the two groups (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). After intervention, both groups showed significant improvements in SSA and OFS scores (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05); the taVNS group had a significant increase in SWAL-QOL scores (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), while the conventional group had no significant change (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05). Intergroup comparison showed no significant differences in SSA and SWAL-QOL scores (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), but the taVNS group had significantly higher OFS scores than the conventional group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). For fNIRS results, in the chewing task, both groups exhibited significantly enhanced activation in the right PFC (RPFC), left PM (LPM), and left M1 (LM1) after intervention (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and the taVNS group had significantly stronger LPM activation than the conventional group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In the tongue tip sliding task, both groups showed significant activation enhancement in LPM, right PM (RPM), LM1, and right S1 (RS1) (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05); additionally, the taVNS group had significant activation increases in right M1 (RM1) and left S1 (LS1) (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with no significant intergroup differences in all brain regions (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). No severe adverse events were observed in either group during the intervention.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003e taVNS combined with routine swallowing rehabilitation is safe and effective for post-stroke oral phase dysphagia, and has a superior effect on improving oral motor function compared with routine rehabilitation alone. The neurophysiological mechanism of taVNS may be related to the enhancement of LPM activation and the promotion of extensive bilateral activation in M1 and S1, which optimizes the activation intensity and pattern of the central swallowing motor-related cortex, thereby facilitating the recovery of oral phase swallowing function. A schematic diagram illustrating this proposed neurophysiological mechanism is presented in Fig.\u0026nbsp;6.\u003c/p\u003e","manuscriptTitle":"Exploring the Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation on Post-Stroke Oral Phase Dysphagia via Functional Near-Infrared Spectroscopy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 10:20:50","doi":"10.21203/rs.3.rs-9073140/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0d6fbfe5-d877-4ae1-81fe-0b6074299c96","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-20T13:57:25+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 10:20:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9073140","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9073140","identity":"rs-9073140","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}