Effects of transcutaneous auricular vagus nerve stimulation on associative memory and event-related potential P300: a single-blind experiment on healthy adults

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The effects of this neuromodulation on associative memory and its mechanisms have not been fully investigated. This crossover, single-blind, active-versus-sham design experiment examined the effects of taVNS on associative memory performance and event-related potential P300, a biomarker of norepinephrine. The experiment consisted of an associative memory task with encoding and retrieval as a set, performed three times with a 10 min rest period, on 14 healthy adults. Participants received taVNS or sham during the 10 min rest between the time 1 and time 2. Event-related potentials were measured at each time of the associative memory task. The washout for this experiment was set at one week. We analyzed the effects of taVNS by means of a general linear mixed model with performance on three associative memory tasks and peak amplitude of event-related potential P300 as dependent variables. The results presented a main effect of taVNS on response time in an associative memory task. We also found a main effect of taVNS on the peak amplitude of event-related potential P300 at Fz, Cz, and Pz. This study indicated that when NE secretion is promoted by taVNS, associative memory performance is enhanced. This noninvasive neuromodulation has potential applications in rehabilitation for cognitive function and should be further investigated for application. Registration : University Hospital Medical Information Network Center (No. UMIN000055911), date: January 24, 2024 “retrospectively registered”. Transcutaneous auricular vagus nerve stimulation associative memory event-related potential rehabilitation Figures Figure 1 Figure 2 Figure 3 Introduction Associative memory (AM) is the ability to rapidly form new connections between two unrelated pieces of information (Yonelinas. 2002; Buchler et al. 2008 ); specifically, by retrieving one piece of information based on another, is indispensable in daily life. Notably, memory function declines with physiological aging and cranial nerve disease (Old et al. 2008; Becker et al. 2015 ). Improvements in AM are important for rehabilitation. Recently, AM rehabilitation has been implemented using various neuromodulation strategies, including non-invasive brain stimulation (Matzen et al. 2015 ; Bjekić et al. 2023 ; Sun et al. 2025 ). Transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulation technique that allows noninvasive vagus nerve stimulation for epileptic seizure treatment; importantly, it has been proposed as a potential intervention for cognitive function improvement, including attention (Ventura-Bort et al. 2018 ), memory (Mertens et al. 2020 ; Kaan et al. 2021 ; Naparstek 2023), and cognitive inhibition (Fischer et al. 2018 ; Zhu et al. 2024 ). Although taVNS’s effects on some cognitive domains have been verified, evidence on taVNS’s impact on AM remains scarce. Jacobs et al. reported that taVNS performed better in AM tasks than did sham in older adults (Jacobs et al. 2015 ). However, that study was limited to measuring AM performance, failing to elucidate the mechanisms underlying performance improvement. Several explanations of taVNS-mediated cognitive function improvement have been proposed. First, aerenchymal nucleus stimulation via the solitary bundle nucleus of the medulla oblongata and activation of noradrenergic and cholinergic neurons of the basal ganglia may release norepinephrine (NE) over a wide area of the neocortex, enhancing cognitive function (Roosevelt et al. 2006 ; Miyashita et al, 2006). This implies that taVNS improves cognitive function domains, including attention, working memory, and concentration (Awh et al. 2006 ; Fischer et al. 2017; Warren et al. 2020 ; Burger et al. 2020 ; Aniwattanapong et al. 2022 ). Second, locus coeruleus (LC) stimulation may directly activate the hippocampus and promote memory formation (McIntyre et al. 2012 ; Mello-Carpes et al. 2013). taVNS’s effect on memory performance has been inconsistent, with some cases exhibiting improved correct response number only, reduced response time, or no impact (Awh et al. 2006 ; Jacobs et al. 2015 ; Mertens et al. 2020 ; Kaan et al. 2021 ; Naparstek et al. 2023 ; Zhao et al. 2023 ). Therefore, understanding which aspects of memory, including AM, are affected by taVNS, will be useful for effective rehabilitation applications. We hypothesized that taVNS’s effect on AM performance would be associated with improved attention and concentration. To test this hypothesis, we confirmed NE secretion along the neocortex. The event-related potential (ERP) P300 is a surrogate biomarker of LC-NE activation (Nieuwenhuis et al. 2005 ; Polich et al. 2007). Additionally, it is commonly used in psychological experiments as a brain activity measure related to cognitive function domains such as attention and concentration (Nieuwenhuis et al. 2005 ; Fischer et al. 2017; Gurtubay et al. 2023 ; Giraudier et al. 2024 ). This study used the ERP P300 to indicate NE changes, measuring it during the AM task; moreover, it tested whether taVNS promoted NE secretion along the neocortex, establishing which AM performance changes occurred. This single-blind crossover study aimed to examine taVNS effects on AM task performance and ERP P300 peak amplitude. Specifically, it investigated (1) which aspects of AM performance taVNS improves (e.g., number of correct responses and response time) and (2) whether taVNS, an NE biomarker, increases the peak amplitude of P300 in frontal-midline (Fz), central-midline (Cz), and parietal-midline (Pz) along the neocortex. Methods Design This study used a crossover single-blind active-versus-sham design and was registered with the University Hospital Medical Information Network Center (UMIN000055911). Participants Fourteen young adults (F8/M6, 21.6 ± 1.4 years) were included. Recruitment involved undergraduate and graduate students at Niigata University of Health and Welfare. The inclusion criteria were as follows: (1) Japanese as the first language; (2) right-handedness according to the Edinburgh Handedness Inventory (Oldfield. 1971); and (3) intelligence quotient of ≥ 80 as measured by the Japanese Adult Reading Test (Matsuoka et al. 2006 ). The exclusion criteria included: (1) history or family history of epileptic seizures; (2) neurological, psychiatric, or cardiac disease; (3) external ear trauma; (4) body implants; (5) regular medication use; (6) pregnancy; and (7) alcohol or drug dependence. All participants abstained from caffeine and other drugs on the day of the experiment. Ethics The study was conducted in accordance with the Declaration of Helsinki, and its protocol was approved by the Institutional Review Board of Niigata University of Health and Welfare (No. 19433–241111). All participants provided written informed consent before participating in the study. Protocol Participants were alternately assigned to two patterns (one or two) in the order of their participation in the experiment (Fig. 1 A). In both patterns, participants had a 1-week washout, with three AM tasks on Days 1 and 8. Pattern 1 participants received taVNS and sham during the first rest period on days 1 and 8, respectively. Pattern 2 participants underwent sham treatment and taVNS during the first rest period on days 1 and 8, respectively. The rest period lasted for 10 min. Salivary amylase was measured before and after the experiment on both days using an sAMY monitor (NIPRO, Osaka, Japan). In addition to the ERP P300, salivary amylase has also been measured as an auxiliary indicator of NE (Burger et al. 2019; D'Agostini et al. 2023 ). At the end of the experiment, the participants were inquired about adverse events and the type of stimulus (taVNS or sham). Transcutaneous auricular vagus nerve stimulation We used taVNS according to minimum reporting standards (Farmer et al. 2021 ). The device used in this study was the tVNS® (NEMOS: tVNS Technologies GmbH, Erlangen, Germany). Stimulation was performed using two titanium electrodes connected to a unit at the auricle (taVNS) or earlobe (sham) (Farmer et al. 2021 ; Yokota. 2024). The electrode was placed on the left side because the vagal nerve on the right side may have caused bradycardia. (Farmer et al. 2021 ; Kim et al. 2022 ; Yuan et al. 2016) (Fig. 1 B). Based on previous research, we applied a stimulus intensity of 0.5 mA, delivered with a pulse width of 200–300 µs at 25 Hz; moreover, stimulation alternated between on and off periods every 30 s (Colzato et al. 2018 ; Mertens et al. 2020 ). The stimulation time was set to 10 min at rest. The participants were checked for adverse events during stimulation, 10 min after stimulation, and 20 min after stimulation. Single blindness was confirmed by listening to the participants’ subjective stimulus types (taVNS or sham) at the end of the experiment. AM task The AM task consisted of encoding and retrieval phases immediately following the encoding phase (Fig. 1 C). The task was created using the Multi-Trigger System (Medical Type System, Tokyo, Japan) and presented to the subjects on a desktop computer screen. The task was conducted in a soundproof room. The participants sat on a chair with a backrest and head support, which was 11.81 inches from the computer used to display the task, and held a button on each hand to perform the task. During the encoding phase, participants learned 50 pairs of Kanji words. Moreover, in the retrieval phase, they were shown the 25 Kanji word pairs presented in the encoding phase (correct) and the 25 Kanji word pairs that were not presented (incorrect); subsequently, they were instructed to press the right and left buttons for “correct” and “incorrect,” respectively. Following each Kanji word-pair presentation, participants had 1 s to relax (black screen) and 1 s to prepare (white plus screen). This task measured the number of correct responses and the response time for each participant. Electroencephalography (EEG) EEG was performed according to the ERP measurement guidelines (Picton et al. 2000 ), using Polymate Pro MP6100 (Miyuki-Giken, Tokyo, Japan). The regions of interest were Fz, Cz, and Pz, in accordance with the international 10–20 system, and the dish electrode was placed using an EEG cap. The reference electrode was positioned on both earlobes. The sampling frequency and band-bus filter were set at 245 Hz and 0.5–30 Hz, respectively. Additionally, the notch filter was set at 50 Hz for preprocessing to remove external interference. Electrooculography was performed to remove the artifacts. During the experiment, we maintained an impedance of less than 5 kΩ between the scalp and the electrode. The ERP analysis was conducted using electromagnetic source estimation (Cortech Solutions, Wilmington, NC, USA). The analysis epoch was set at 2000 ms after Kanji word pair presentation, and averaging was performed after artifact removal. Notably, taVNS may affect the ERP P300 (Fischer et al. 2018 ; Giraudier et al. 2024 ), which is an alternative representation of brain activity associated with cognitive processing (Polich et al. 1995; Polich et al. 2004). Here, based on previous studies, the P300 was defined as 250–400 ms following stimulus presentation, and its peak amplitude was measured (Fischer et al. 2018 ; Fields 2023 ). Statistical analysis Statistical analyses were conducted using the IBM Statistical Package for the Social Sciences Statistics for Windows (version 27.0; IBM Corp, Armonk, NY). The significance level was set at p < 0.05. All measured AM performance and ERP P300 are presented as mean ± standard deviation. Pairwise t-tests (bilateral) were used to compare variables between the taVNS and sham groups at each time point. Verification of effectiveness of taVNS: generalized linear mixed model A general linear mixed-effects model tested the effects of stimulus type on AM performance and ERP P300. We confirmed the non-normality of the dependent variable errors before running the generalized linear mixed model. The dependent variables included the number of correct responses and response times for the AM task and the peak amplitude of P300 in Fz, Cz, and Pz. Fixed effects were defined as stimulus (taVNS or sham) and session (Time 1, Time 2, and Time 3), and random factors included the subject ID. The focus was on the main effect of the stimulus on each dependent variable. Changes in salivary amylase: paired t-test A paired t-test compared changes in salivary amylase levels before and after the experiment to examine. Single-blind validation: chi-square test Chi-square tests compared each participant's subjective stimulus type (taVNS or sham) and actual stimulus type (taVNS or sham). Results Associative memory performance and event-related potentials in participants The experiments were performed without missing data or exclusion criteria. None of the participants reported adverse events. A summary of each participant's AM performance and ERP P300 is presented in Table 1 and Figs. 2 and 3 . The ERP P300 of the Fz, Cz, and Pz during the AM task increased in peak amplitude with each repetition of the AM task in the taVNS group (Fig. 3 ). However, pairwise t-tests did not show significant differences for any variable (Table 1 ). Table 1 A summary of each participant's associative memory performance and ERP P300 taVNS Sham p Associative memory performance The number of correct Time 1 37.1 ± 7.7 33.8 ± 9.5 0.213 Time 2 39.71 ± 6.7 37.5 ± 8.4 0.173 Time 3 42.2 ± 6.4 41.5 ± 7.3 0.583 Response time (ms) Time 1 1267.7 ± 495.1 1223.1 ± 458.8 0.589 Time 2 993 ± 290.3 1145.1 ± 393.0 0.089 Time 3 888.0 ± 170.3 1010.2 ± 318.4 0.094 ERP P300 Fz P300 peak amplitude (µV) Time 1 6.6 ± 11.1 8.2 ± 11.4 0.305 Time 2 5.7 ± 10.8 5.7 ± 10.0 0.991 Time 3 8.8 ± 14.8 6.0 ± 9.8 0.533 Cz P300 peak amplitude (µV) Time 1 6.6 ± 13.4 7.5 ± 13.5 0.599 Time 2 6.0 ± 13.0 7.0 ± 11.7 0.740 Time 3 9.7 ± 15.9 7.0 ± 10.5 0.567 Pz P300 peak amplitude (µV) Time 1 8.1 ± 13.3 12.1 ± 14.9 0.050 Time 2 10.8 ± 14.5 10.3 ± 13.5 0.893 Time 3 13.7 ± 16.9 10.6 ± 11.2 0.508 Mean ± standard deviation. taVNS, transcutaneous auricular vagus nerve stimulation; ERP, event-related potential. Verification of effectiveness of taVNS Table 2 presents taVNS’s effect on performance and ERP P300 during AM task repetitions. The general linear mixed model demonstrated a main effect of taVNS on response time in the AM task ( β : -545.755, 95% confidence interval (CI): -1002.736 to -88.775, p = 0.018), highlighting that taVNS effectively reduced response time in the AM task compared to the sham task. ERP P300 exhibited a main effect of taVNS on Fz ( β : 26.215, 95% CI: 13.762 to 38.667, p < 0.001), Cz ( β : 28.059, 95% CI: 13.823 to 42.295, p < 0.001), and Pz ( β : 31.981, 95% CI: 16.173 to 47.789, p < 0.001), indicating that ERP P300’s peak amplitude increased with AM task repetition in the taVNS group compared to the sham group. Table 2 Verification of effectiveness of taVNS β β SE 95% CI Wald p AM performance: number of correct responses Stimulation 7.660 4.567 -1.292 to 16.612 2.812 0.094 Time 1.286 2.794 -4.192 to 6.764 0.212 0.645 Stimulation*time 1.286 1.767 -2.179 to 4.750 0.529 0.467 AM performance: response time Stimulation -545.755 230.497 -1002.736 to -88.775 5.606 0.018 Time -273.236 141.0416 -552.863 to 6.391 3.753 0.053 Stimulation*time 83.404 89.202 -93.448 to 260.255 0.874 0.350 ERP P300: Fz Stimulation 26.215 6.353 13.762 to 38.667 17.025 < 0.001 Time 3.273 3.887 -4.346 to 10.893 0.709 0.400 Stimulation*time -2.190 2.458 -7.009 to 2.629 0.793 0.373 ERP P300: Cz Stimulation 28.059 7.263 13.823 to 42.295 14.924 < 0.001 Time 3.346 4.444 -5.365 to 12.057 0.567 0.452 Stimulation*time -1.791 2.810 -7.301 to 3.718 0.406 0.524 ERP P300: Pz Stimulation 31.981 8.065 16.173 to 47.789 15.723 < 0.001 Time 6.274 4.935 -3.399 to 15.947 1.616 0.204 Stimulation*time -3.498 0.316 -9.161 to 2.620 1.256 0.262 Stimulation (1: transcutaneous auricular vagus nerve stimulation; 2: sham). Time (1: Time 1; 2: Time 2; 3: Time 3). 95% CI, 95% confidence interval; AM, associative memory; ERP, event-related potential. Changes in salivary amylase Table 4 displays the absence of changes in salivary amylase levels before and after stimulation. Table 4 Changes in salivary amylase Pre Post p Transcutaneous auricular vagus nerve stimulation 38.6 ± 42.8 47.3 ± 52.5 0.214 Sham 53.0 ± 42.8 50.0 ± 34.5 0.594 Mean ± standard deviation. Single-blind validation Table 5 summarizes each participant’s subjective ratings of stimulus type at the end of the experiment. The chi-squared analysis revealed no statistically significant differences, suggesting the integrity of the single-blind design. Table 5 Single-blind validation: chi-square test Stimulation type p taVNS Sham Subjective stimulation type taVNS 4 7 0.440 Sham 10 7 taVNS: Transcutaneous auricular vagus nerve stimulation Discussion This crossover, single-blind, active versus sham experiment demonstrated that taVNS increased the ERP P300 peak amplitude and reduced the response time during the AM task compared to the sham using a general linear mixed model. Therefore, we speculate that taVNS secreted NE in neocortical regions and enhanced AM task performance. The ERP P300 peak amplitude is sensitive to the noradrenergic system and is considered an indicator of LC-NE activation (Brown et al. 2015 ; Badran et al. 2018 ; Burger et al. 2020 ). Furthermore, it is also used as evidence that taVNS enhances cognitive aspects such as memory, attention, and cognitive inhibition (Fischer et al. 2017; Warren et al. 2020 ; Burger et al. 2020 ). This is explained by the LC-P300 theory, which states that NE secreted from the LC activates the entire neocortex (Nieuwenhuis et al. 2005 ). Several studies reported increases in the P300 peak amplitude and cognitive performance with taVNS (Fischer et al. 2017; Gurtubay et al. 2023 ; Giraudier et al, 2024 ); nonetheless, they were limited to measuring P300 in only one region. Interestingly, we measured the Fz, Cz, and Pz regions along the neocortex and found an increase in P300 peak amplitude in these regions, providing evidence for a relationship between taVNS and the LC-P300 theory. This study demonstrated the effect of taVNS on response time reduction during AM tasks. The LC-P300 theory is based on the NE activation within the frontoparietal attention network (Nieuwenhuis et al. 2005 ). Importantly, our findings corroborate those of previous studies that reported improved response times in various cognitive tasks (Nieuwenhuis et al. 2005 ; Rufener et al. 2018 ; Wienke et al. 2023 ). The lack of change in the number of correct responses observed in our study suggests that taVNS may enhance attentional function rather than memory (Mertens et al. 2020 ; Kaan et al. 2021 ; Naparstek 2023). Kaan et al. examined taVNS’s effects on verbal memory demonstrating improved performance over sham only in tasks with high demands for attention and inhibition (Kaan et al. 2021 ). Furthermore, Zhao et al. showed that taVNS improved working memory performance in sleep-deprived subjects; nevertheless, this may have resulted from increased arousal (Zhao et al. 2023 ). Here, the fact that taVNS did not improve the number of correct responses while reducing response time may be due to enhanced attentional function rather than enhanced memory. However, substantial research reported that taVNS enhances memory performance in older adults with mild cognitive impairment and epilepsy (Jacobs et al. 2015 ; Wang et al. 2022 ; Pan et al. 2024 ; Szeska et al. 2025 ; An et al. 2025 ). Specifically, Jacobs et al.’s single-arm study reported an increased number of correct responses in an AM task following taVNS in older adults (Jacobs et al. 2015 ). This may be explained by the fact that subjects with cognitive decline may be more likely to benefit from taVNS owing to sympathetic dominance and decreased NE secretion (Broncel et al, 2020 ; Naparstek et al. 2023 ). Additionally, the healthy adults in this study may have exhibited a ceiling effect on the memory task because their cognitive functions were intact (Mertens et al. 2020 ; Naparstek 2023; An et al. 2025 ). Previously, we observed a ceiling effect when an AM task was repeated (Sun et al. 2025 ). Therefore, the effects of taVNS on memory tasks warrant further investigation. This study was conducted with a constant stimulus intensity (0.5 mV) for all subjects based on previous research; this differs from threshold method used in many other studies to set the stimulus intensity (Beste et al. 2016 ; Colzato et al. 2018 ; Mertens et al. 2020 ). Our stimulus intensity may have been weaker for some participants compared with that of the threshold method. Here, taVNS’s effect was confirmed by general linear mixed effects with individuals as random effects, indicating that some subjects may have not benefited from taVNS. Nonetheless, no adverse events typically identified in taVNS studies, such as prickling, were reported by our participants, supporting safe and effective taVNS. Further experiments to determine optimal taVNS settings are warranted. Limitations This study had some limitations. First, the carryover effect, which is often present in crossover designs, should be taken into account. Nevertheless, AM performance and peak amplitude of ERP at Time 1 did not differ significantly between groups. Furthermore, recent studies have shown that taVNS may not exhibit a carryover effect over time (Miyatsu et al. 2024 ). Second, the absence of a main effect of taVNS on the number of correct responses may be related to the floor-ceiling effect of the task. Finally, salivary amylase levels may be an inappropriate surrogate marker of NE; recent studies recommend P300 or pupil diameter as a measure of NE changes (Villani et al. 2022 ; Wienke et al. 2023 ). Conclusion This study examined the effects of taVNS on AM performance and ERP P300. This study indicated that taVNS increased the P300 peak amplitude at Fz, Cz, and Pz in the neocortex and reduced response time in the AM task. Our results provide data to support the effect of taVNS on AM. Because neuromodulation is noninvasive and simple, its application in the rehabilitation of cognitive function is desirable. For clinical applications, the effects of taVNS on cognitive function and optimal application methods should be continuously investigated. Declarations Funding This work was supported by JSPS KAKENHI Grant-in-Aid for Early-Career Scientists Number 24K20544. Competing interests The authors declare no competing interests. Author contributions Conceptualization: H.A; Methodology: H.A; Formal analysis and investigation: H.A, M.S, and T.H; Writing - original draft preparation: H.A; Writing - review and editing: H.A, M,S, T.H, and T.N; Funding acquisition: H.A; Resources: H.A; Supervision: H.A. Ethics approval The study was conducted in accordance with the Declaration of Helsinki, and its protocol was approved by the Institutional Review Board of Niigata University of Health and Welfare (No. 19433-241111). Informed consent All participants provided written informed consent prior to participation in the experiment. Data availability Data from this experiment can be found in Appendix 1. 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B., Izquierdo, I (2013) The Nucleus of the Solitary Tract → Nucleus Paragigantocellularis → Locus Coeruleus → CA1 region of dorsal hippocampus pathway is important for consolidation of object recognition memory. Neurobiology of learning and memory 100:56–63. https://doi.org/10.1016/j.nlm.2012.12.002 Mertens, A., Naert, L., Miatton, M et al (2020). Transcutaneous Vagus Nerve Stimulation Does Not Affect Verbal Memory Performance in Healthy Volunteers. Frontiers in psychology 11:551. https://doi.org/10.3389/fpsyg.2020.00551 Miyashita, T., & Williams, C. L (2006) Epinephrine administration increases neural impulses propagated along the vagus nerve: Role of peripheral beta-adrenergic receptors. Neurobiology of learning and memory 85:116–124. https://doi.org/10.1016/j.nlm.2005.08.013 Miyatsu, T., Oviedo, V., Reynaga, J., Karuzis, V. P., Martinez, D., O'Rourke, P et al (2024) Transcutaneous cervical vagus nerve stimulation enhances second-language vocabulary acquisition while simultaneously mitigating fatigue and promoting focus. Scientific reports 14:17177. https://doi.org/10.1038/s41598-024-68015-4 Naparstek, S., Yeh, A. K., Mills-Finnerty, C (2023) Transcutaneous Vagus Nerve Stimulation (tVNS) applications in cognitive aging: a review and commentary. Frontiers in aging neuroscience 15:1145207. https://doi.org/10.3389/fnagi.2023.1145207 Nieuwenhuis, S., Aston-Jones, G., Cohen, J. D (2005) Decision making, the P3, and the locus coeruleus-norepinephrine system. Psychological bulletin 131:510–532. https://doi.org/10.1037/0033-2909.131.4.510 Old, S. R., & Naveh-Benjamin, M (2008) Differential effects of age on item and associative measures of memory: a meta-analysis. Psychology and aging 23:104–118. https://doi.org/10.1037/0882-7974.23.1.104 Oldfield RC (1971) The assessment and analysis of handedness: The Edinburgh inventory. Neuropsychologia 9:97-113. https://doi.org/10.1016/0028-3932(71)90067-4 Pan, L., Wang, J., Wu, W., Wang, Y., Zhu, Y., Song, Y (2024) Transcutaneous auricular vagus nerve stimulation improves working memory in temporal lobe epilepsy: A randomized double-blind study. CNS neuroscience & therapeutics 30:e14395. https://doi.org/10.1111/cns.14395 Picton, T. W., Bentin, S., Berg, P et al (2000) Guidelines for using human event-related potentials to study cognition: recording standards and publication criteria. Psychophysiology 37:127–152. Polich, J., & Kok, A (1995) Cognitive and biological determinants of P300: an integrative review. Biological psychology 41:103–146. https://doi.org/10.1016/0301-0511(95)05130-9 Polich J (2004) Clinical application of the P300 event-related brain potential. Physical medicine and rehabilitation clinics of North America 15:133–161. https://doi.org/10.1016/s1047-9651(03)00109-8 Polich J (2007). Updating P300: an integrative theory of P3a and P3b. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 118:2128–2148. https://doi.org/10.1016/j.clinph.2007.04.019 Roosevelt, R. W., Smith, D. C., Clough, R. W., Jensen, R. A., Browning, R. A (2006) Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat. Brain research 1119:124–132. https://doi.org/10.1016/j.brainres.2006.08.048 Rufener, K. S., Geyer, U., Janitzky, K., Heinze, H. J., Zaehle, T (2018) Modulating auditory selective attention by non-invasive brain stimulation: Differential effects of transcutaneous vagal nerve stimulation and transcranial random noise stimulation. The European journal of neuroscience 48:2301–2309. https://doi.org/10.1111/ejn.14128 Sun, S., Annaka, H., Nomura, T (2025) Gamma-frequency transcranial alternating current stimulation over the left posterior parietal cortex enhances the long-term retention of associative memory. Experimental brain research 243:62. https://doi.org/10.1007/s00221-025-07009-8 Szeska, C., Ventura-Bort, C., Giraudier, M., Weymar, M (2025) A vagal route to memory: evidence from invasive and non-invasive electrical vagus nerve stimulation studies and areas for future clinical application. Frontiers in Human Neuroscience 19:2025. 10.3389/fnhum.2025.1595737 Ventura-Bort, C., Wirkner, J., Genheimer, H., Wendt, J., Hamm, A. O., Weymar, M (2018) Effects of Transcutaneous Vagus Nerve Stimulation (tVNS) on the P300 and Alpha-Amylase Level: A Pilot Study. Frontiers in human neuroscience 12:202. https://doi.org/10.3389/fnhum.2018.00202 Villani, V., Finotti, G., Di Lernia, D., Tsakiris, M., & Azevedo, R. T (2022) Event-related transcutaneous vagus nerve stimulation modulates behaviour and pupillary responses during an auditory oddball task. Psychoneuroendocrinology 140:105719. https://doi.org/10.1016/j.psyneuen.2022.105719 Wang, L., Zhang, J., Guo, C et al (2022) The efficacy and safety of transcutaneous auricular vagus nerve stimulation in patients with mild cognitive impairment: A double blinded randomized clinical trial. Brain stimulation 15:1405–1414. https://doi.org/10.1016/j.brs.2022.09.003 Warren, C. V., Maraver, M. J., de Luca, A., Kopp, B (2020). The Effect of Transcutaneous Auricular Vagal Nerve Stimulation (taVNS) on P3 Event-Related Potentials during a Bayesian Oddball Task. Brain sciences 10:404. https://doi.org/10.3390/brainsci10060404 Wienke, C., Grueschow, M., Haghikia, A., Zaehle, T (2023) Phasic, Event-Related Transcutaneous Auricular Vagus Nerve Stimulation Modifies Behavioral, Pupillary, and Low-Frequency Oscillatory Power Responses. The Journal of neuroscience : the official journal of the Society for Neuroscience 43:6306–6319. https://doi.org/10.1523/JNEUROSCI.0452-23.2023 Yonelinas, A. P (2002) The nature of recollection and familiarity: A review of 30 years of research. Journal of Memory and Language 46:441–517. https://doi.org/10.1006/jmla.2002.2864 Yokota, H., Edama, M., Kawanabe, Y et al (2024) Effects of transcutaneous auricular vagus nerve stimulation at left cymba concha on experimental pain as assessed with the nociceptive withdrawal reflex, and correlation with parasympathetic activity. The European journal of neuroscience 59:2826–2835. https://doi.org/10.1111/ejn.16305 Yuan, H., & Silberstein, S. D (2016). Vagus Nerve and Vagus Nerve Stimulation, a Comprehensive Review: Part II. Headache 56:259–266. https://doi.org/10.1111/head.12650 Zhao, R., Chang, M. Y., Cheng, C et al (2023) Transcutaneous auricular vagus stimulation (taVNS) improves human working memory performance under sleep deprivation stress. Behavioural brain research 439:114247. https://doi.org/10.1016/j.bbr.2022.114247 Zhu, S., Liu, Q., Zhang, X et al (2024) Transcutaneous auricular vagus nerve stimulation enhanced emotional inhibitory control via increasing intrinsic prefrontal couplings. International journal of clinical and health psychology : IJCHP 24:100462. https://doi.org/10.1016/j.ijchp.2024.100462 Additional Declarations No competing interests reported. Supplementary Files appendix1.xlsx Appendix 1: Dataset for this experiment. Cite Share Download PDF Status: Published Journal Publication published 05 Oct, 2025 Read the published version in Experimental Brain Research → 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. 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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-7263208","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":496144192,"identity":"abedc8c4-9723-490a-b961-331d59120e4c","order_by":0,"name":"Hiroki Annaka","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYBACA2YGBsYGAzCbGUTIgYgDD0jRYgzWkoBPCwNICwNCSyKYg0+LOTvvw4czChjkzaWbHxv8YLiTPj/s8EOgLXZyug3YtVg2sxsbbjBgMNw555hxYg/Ds9yNt9MMgFqSjc0O4HDYYTY2yQcGDIwbbiQYH+BhOJy7cXYCSMuBxG0EtNhvuJH++eAfhsPphrPTPxDWAnRY4oYbOcbJQFsS5KVzCNrCbDjDQCIZqKXYWMbgsOEG6ZyCAwkGePxy/hjjw54/NrZAh22WfFNxWF5+dvrmDx8q7ORwaYECCZgJQHQAyiAeyDeQonoUjIJRMApGAgAATn1e+RxUrdsAAAAASUVORK5CYII=","orcid":"","institution":"Niigata University of Health and Welfare","correspondingAuthor":true,"prefix":"","firstName":"Hiroki","middleName":"","lastName":"Annaka","suffix":""},{"id":496144193,"identity":"a5f7daad-00fa-46d9-8090-2f8df8126270","order_by":1,"name":"Misaki Saitou","email":"","orcid":"","institution":"Niigata University of Health and Welfare","correspondingAuthor":false,"prefix":"","firstName":"Misaki","middleName":"","lastName":"Saitou","suffix":""},{"id":496144194,"identity":"cad5610a-4d0b-44e1-ae72-4d57c356ccbb","order_by":2,"name":"Tamon Hiraoka","email":"","orcid":"","institution":"Niigata University of Health and Welfare","correspondingAuthor":false,"prefix":"","firstName":"Tamon","middleName":"","lastName":"Hiraoka","suffix":""},{"id":496144195,"identity":"a3049c41-299a-4d20-9554-5e06d3d2d2d8","order_by":3,"name":"Tomonori Nomura","email":"","orcid":"","institution":"Niigata University of Health and Welfare","correspondingAuthor":false,"prefix":"","firstName":"Tomonori","middleName":"","lastName":"Nomura","suffix":""}],"badges":[],"createdAt":"2025-07-31 14:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7263208/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7263208/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00221-025-07171-z","type":"published","date":"2025-10-05T15:58:03+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":88642194,"identity":"9fe7fbb0-a49e-4181-9422-ab882856a501","added_by":"auto","created_at":"2025-08-08 16:11:38","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":293828,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental protocol. Participants were assigned to pattern 1 (P1) or pattern 2 (P2) in order of participation; P1 received taVNS and sham on days 1 and 8, respectively, while P2 did so on days 1 and 8, respectively (A). Stimulation electrodes were placed on the auricle and earlobe for taVNS and sham, respectively (B). In the AM task, subjects were asked to learn 50 pairs of Kanji words in the encoding phase, immediately followed by a retrieval phase in which the 25 pairs shown in the encoding phase were presented as correct stimuli, whereas the 25 novel pairs were presented as incorrect stimuli (C). P1: pattern 1, P2: pattern 2, AM task: associative memory task, taVNS: Transcutaneous auricular vagus nerve stimulation, EEG: electroencephalography.\u003c/p\u003e","description":"","filename":"Fig.1..tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7263208/v1/e857e0898e739661371fb2a8.jpg"},{"id":88642197,"identity":"a464315d-ebd5-4947-9245-0808cfc56e2b","added_by":"auto","created_at":"2025-08-08 16:11:39","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":298704,"visible":true,"origin":"","legend":"\u003cp\u003ePlot summary of associative memory performance. A: Number of correct responses. The higher the position on the y-axis, the better the performance. B: Response time. The lower the position on the y-axis, the better the performance. Black line: plot of mean performance. Blue line: plot of each participant’s performance.\u003c/p\u003e","description":"","filename":"Fig.2..tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7263208/v1/dc03d7dbd0cf457503425fca.jpg"},{"id":88642193,"identity":"692e7f7f-a8e3-4e00-9c09-af2366e5210f","added_by":"auto","created_at":"2025-08-08 16:11:38","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":262304,"visible":true,"origin":"","legend":"\u003cp\u003eTrends in ERP P300 during an associative memory task. In the transcutaneous auricular vagus nerve stimulation, the P300 peak amplitude increased compared to that of sham. A: Fz. B: Cz. C: Pz. P300 epoch: 250–400 ms.\u003c/p\u003e","description":"","filename":"Fig.3..tif.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7263208/v1/1a2d1737fb8e9500f11fa94c.jpg"},{"id":92884661,"identity":"f783fe87-7e3d-4936-b971-d2df821bc34b","added_by":"auto","created_at":"2025-10-06 16:13:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1600880,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7263208/v1/b7c3f9a7-ab67-475e-84e6-3cd6901dd3c2.pdf"},{"id":88644139,"identity":"00abda40-1c48-4cc3-afa3-399d8e72b7bc","added_by":"auto","created_at":"2025-08-08 16:19:38","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14198,"visible":true,"origin":"","legend":"\u003cp\u003eAppendix 1: Dataset for this experiment.\u003c/p\u003e","description":"","filename":"appendix1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7263208/v1/8c10f558ee94e233b812336a.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of transcutaneous auricular vagus nerve stimulation on associative memory and event-related potential P300: a single-blind experiment on healthy adults","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAssociative memory (AM) is the ability to rapidly form new connections between two unrelated pieces of information (Yonelinas. 2002; Buchler et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e); specifically, by retrieving one piece of information based on another, is indispensable in daily life. Notably, memory function declines with physiological aging and cranial nerve disease (Old et al. 2008; Becker et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Improvements in AM are important for rehabilitation. Recently, AM rehabilitation has been implemented using various neuromodulation strategies, including non-invasive brain stimulation (Matzen et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Bjekić et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Sun et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eTranscutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulation technique that allows noninvasive vagus nerve stimulation for epileptic seizure treatment; importantly, it has been proposed as a potential intervention for cognitive function improvement, including attention (Ventura-Bort et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), memory (Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kaan et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Naparstek 2023), and cognitive inhibition (Fischer et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Although taVNS’s effects on some cognitive domains have been verified, evidence on taVNS’s impact on AM remains scarce. Jacobs et al. reported that taVNS performed better in AM tasks than did sham in older adults (Jacobs et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). However, that study was limited to measuring AM performance, failing to elucidate the mechanisms underlying performance improvement. Several explanations of taVNS-mediated cognitive function improvement have been proposed. First, aerenchymal nucleus stimulation via the solitary bundle nucleus of the medulla oblongata and activation of noradrenergic and cholinergic neurons of the basal ganglia may release norepinephrine (NE) over a wide area of the neocortex, enhancing cognitive function (Roosevelt et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Miyashita et al, 2006). This implies that taVNS improves cognitive function domains, including attention, working memory, and concentration (Awh et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Fischer et al. 2017; Warren et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Burger et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Aniwattanapong et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Second, locus coeruleus (LC) stimulation may directly activate the hippocampus and promote memory formation (McIntyre et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Mello-Carpes et al. 2013). taVNS’s effect on memory performance has been inconsistent, with some cases exhibiting improved correct response number only, reduced response time, or no impact (Awh et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Jacobs et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kaan et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Naparstek et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Zhao et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Therefore, understanding which aspects of memory, including AM, are affected by taVNS, will be useful for effective rehabilitation applications.\u003c/p\u003e\u003cp\u003eWe hypothesized that taVNS’s effect on AM performance would be associated with improved attention and concentration. To test this hypothesis, we confirmed NE secretion along the neocortex. The event-related potential (ERP) P300 is a surrogate biomarker of LC-NE activation (Nieuwenhuis et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Polich et al. 2007). Additionally, it is commonly used in psychological experiments as a brain activity measure related to cognitive function domains such as attention and concentration (Nieuwenhuis et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Fischer et al. 2017; Gurtubay et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Giraudier et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This study used the ERP P300 to indicate NE changes, measuring it during the AM task; moreover, it tested whether taVNS promoted NE secretion along the neocortex, establishing which AM performance changes occurred.\u003c/p\u003e\u003cp\u003eThis single-blind crossover study aimed to examine taVNS effects on AM task performance and ERP P300 peak amplitude. Specifically, it investigated (1) which aspects of AM performance taVNS improves (e.g., number of correct responses and response time) and (2) whether taVNS, an NE biomarker, increases the peak amplitude of P300 in frontal-midline (Fz), central-midline (Cz), and parietal-midline (Pz) along the neocortex.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cb\u003eDesign\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis study used a crossover single-blind active-versus-sham design and was registered with the University Hospital Medical Information Network Center (UMIN000055911).\u003c/p\u003e\u003cp\u003e\u003cb\u003eParticipants\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFourteen young adults (F8/M6, 21.6 ± 1.4 years) were included. Recruitment involved undergraduate and graduate students at Niigata University of Health and Welfare. The inclusion criteria were as follows: (1) Japanese as the first language; (2) right-handedness according to the Edinburgh Handedness Inventory (Oldfield. 1971); and (3) intelligence quotient of ≥ 80 as measured by the Japanese Adult Reading Test (Matsuoka et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The exclusion criteria included: (1) history or family history of epileptic seizures; (2) neurological, psychiatric, or cardiac disease; (3) external ear trauma; (4) body implants; (5) regular medication use; (6) pregnancy; and (7) alcohol or drug dependence. All participants abstained from caffeine and other drugs on the day of the experiment.\u003c/p\u003e\u003cp\u003e\u003cb\u003eEthics\u003c/b\u003e\u003c/p\u003e\u003cp\u003e The study was conducted in accordance with the Declaration of Helsinki, and its protocol was approved by the Institutional Review Board of Niigata University of Health and Welfare (No. 19433–241111). All participants provided written informed consent before participating in the study.\u003c/p\u003e\u003cp\u003e\u003cb\u003eProtocol\u003c/b\u003e\u003c/p\u003e\u003cp\u003eParticipants were alternately assigned to two patterns (one or two) in the order of their participation in the experiment (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). In both patterns, participants had a 1-week washout, with three AM tasks on Days 1 and 8. Pattern 1 participants received taVNS and sham during the first rest period on days 1 and 8, respectively. Pattern 2 participants underwent sham treatment and taVNS during the first rest period on days 1 and 8, respectively. The rest period lasted for 10 min. Salivary amylase was measured before and after the experiment on both days using an sAMY monitor (NIPRO, Osaka, Japan). In addition to the ERP P300, salivary amylase has also been measured as an auxiliary indicator of NE (Burger et al. 2019; D'Agostini et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). At the end of the experiment, the participants were inquired about adverse events and the type of stimulus (taVNS or sham).\u003c/p\u003e\u003cp\u003e\u003cb\u003eTranscutaneous auricular vagus nerve stimulation\u003c/b\u003e\u003c/p\u003e\u003cp\u003eWe used taVNS according to minimum reporting standards (Farmer et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The device used in this study was the tVNS® (NEMOS: tVNS Technologies GmbH, Erlangen, Germany). Stimulation was performed using two titanium electrodes connected to a unit at the auricle (taVNS) or earlobe (sham) (Farmer et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Yokota. 2024). The electrode was placed on the left side because the vagal nerve on the right side may have caused bradycardia. (Farmer et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Kim et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yuan et al. 2016) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). Based on previous research, we applied a stimulus intensity of 0.5 mA, delivered with a pulse width of 200–300 µs at 25 Hz; moreover, stimulation alternated between on and off periods every 30 s (Colzato et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The stimulation time was set to 10 min at rest. The participants were checked for adverse events during stimulation, 10 min after stimulation, and 20 min after stimulation. Single blindness was confirmed by listening to the participants’ subjective stimulus types (taVNS or sham) at the end of the experiment.\u003c/p\u003e\u003cp\u003e\u003cb\u003eAM task\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe AM task consisted of encoding and retrieval phases immediately following the encoding phase (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). The task was created using the Multi-Trigger System (Medical Type System, Tokyo, Japan) and presented to the subjects on a desktop computer screen. The task was conducted in a soundproof room. The participants sat on a chair with a backrest and head support, which was 11.81 inches from the computer used to display the task, and held a button on each hand to perform the task.\u003c/p\u003e\u003cp\u003e During the encoding phase, participants learned 50 pairs of Kanji words. Moreover, in the retrieval phase, they were shown the 25 Kanji word pairs presented in the encoding phase (correct) and the 25 Kanji word pairs that were not presented (incorrect); subsequently, they were instructed to press the right and left buttons for “correct” and “incorrect,” respectively. Following each Kanji word-pair presentation, participants had 1 s to relax (black screen) and 1 s to prepare (white plus screen). This task measured the number of correct responses and the response time for each participant.\u003c/p\u003e\u003cp\u003e\u003cb\u003eElectroencephalography (EEG)\u003c/b\u003e\u003c/p\u003e\u003cp\u003e EEG was performed according to the ERP measurement guidelines (Picton et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), using Polymate Pro MP6100 (Miyuki-Giken, Tokyo, Japan). The regions of interest were Fz, Cz, and Pz, in accordance with the international 10–20 system, and the dish electrode was placed using an EEG cap. The reference electrode was positioned on both earlobes. The sampling frequency and band-bus filter were set at 245 Hz and 0.5–30 Hz, respectively. Additionally, the notch filter was set at 50 Hz for preprocessing to remove external interference. Electrooculography was performed to remove the artifacts. During the experiment, we maintained an impedance of less than 5 kΩ between the scalp and the electrode.\u003c/p\u003e\u003cp\u003eThe ERP analysis was conducted using electromagnetic source estimation (Cortech Solutions, Wilmington, NC, USA). The analysis epoch was set at 2000 ms after Kanji word pair presentation, and averaging was performed after artifact removal. Notably, taVNS may affect the ERP P300 (Fischer et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Giraudier et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), which is an alternative representation of brain activity associated with cognitive processing (Polich et al. 1995; Polich et al. 2004). Here, based on previous studies, the P300 was defined as 250–400 ms following stimulus presentation, and its peak amplitude was measured (Fischer et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Fields \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e\u003ch2\u003eStatistical analysis\u003c/h2\u003e\u003cp\u003eStatistical analyses were conducted using the IBM Statistical Package for the Social Sciences Statistics for Windows (version 27.0; IBM Corp, Armonk, NY). The significance level was set at p \u0026lt; 0.05. All measured AM performance and ERP P300 are presented as mean ± standard deviation. Pairwise t-tests (bilateral) were used to compare variables between the taVNS and sham groups at each time point.\u003c/p\u003e\u003cp\u003e\u003cem\u003eVerification of effectiveness of taVNS: generalized linear mixed model\u003c/em\u003e\u003c/p\u003e\u003cp\u003eA general linear mixed-effects model tested the effects of stimulus type on AM performance and ERP P300. We confirmed the non-normality of the dependent variable errors before running the generalized linear mixed model. The dependent variables included the number of correct responses and response times for the AM task and the peak amplitude of P300 in Fz, Cz, and Pz. Fixed effects were defined as stimulus (taVNS or sham) and session (Time 1, Time 2, and Time 3), and random factors included the subject ID. The focus was on the main effect of the stimulus on each dependent variable.\u003c/p\u003e\u003cp\u003e\u003cem\u003eChanges in salivary amylase: paired t-test\u003c/em\u003e\u003c/p\u003e\u003cp\u003eA paired t-test compared changes in salivary amylase levels before and after the experiment to examine.\u003c/p\u003e\u003cp\u003e\u003cem\u003eSingle-blind validation: chi-square test\u003c/em\u003e\u003c/p\u003e\u003cp\u003eChi-square tests compared each participant's subjective stimulus type (taVNS or sham) and actual stimulus type (taVNS or sham).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cb\u003eAssociative memory performance and event-related potentials in participants\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThe experiments were performed without missing data or exclusion criteria. None of the participants reported adverse events.\u003c/p\u003e\u003cp\u003eA summary of each participant's AM performance and ERP P300 is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The ERP P300 of the Fz, Cz, and Pz during the AM task increased in peak amplitude with each repetition of the AM task in the taVNS group (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). However, pairwise t-tests did not show significant differences for any variable (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\u003eA summary of each participant's associative memory performance and ERP P300\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003etaVNS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSham\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ep\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAssociative memory performance\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThe number of correct\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e37.1\u0026thinsp;\u0026plusmn;\u0026thinsp;7.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e33.8\u0026thinsp;\u0026plusmn;\u0026thinsp;9.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.213\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e39.71\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e37.5\u0026thinsp;\u0026plusmn;\u0026thinsp;8.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.173\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e42.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e41.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.583\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eResponse time (ms)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e1267.7\u0026thinsp;\u0026plusmn;\u0026thinsp;495.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1223.1\u0026thinsp;\u0026plusmn;\u0026thinsp;458.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.589\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e993\u0026thinsp;\u0026plusmn;\u0026thinsp;290.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1145.1\u0026thinsp;\u0026plusmn;\u0026thinsp;393.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.089\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e888.0\u0026thinsp;\u0026plusmn;\u0026thinsp;170.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e1010.2\u0026thinsp;\u0026plusmn;\u0026thinsp;318.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.094\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eERP P300\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFz P300 peak amplitude (\u0026micro;V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;11.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;11.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.305\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;10.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e5.7\u0026thinsp;\u0026plusmn;\u0026thinsp;10.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.991\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e8.8\u0026thinsp;\u0026plusmn;\u0026thinsp;14.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;9.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.533\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCz P300 peak amplitude (\u0026micro;V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;13.4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.599\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;13.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;11.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.740\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e9.7\u0026thinsp;\u0026plusmn;\u0026thinsp;15.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;10.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.567\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePz P300 peak amplitude (\u0026micro;V)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e8.1\u0026thinsp;\u0026plusmn;\u0026thinsp;13.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e12.1\u0026thinsp;\u0026plusmn;\u0026thinsp;14.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.050\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e10.8\u0026thinsp;\u0026plusmn;\u0026thinsp;14.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e10.3\u0026thinsp;\u0026plusmn;\u0026thinsp;13.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.893\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e\u003cp\u003e13.7\u0026thinsp;\u0026plusmn;\u0026thinsp;16.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e\u003cp\u003e10.6\u0026thinsp;\u0026plusmn;\u0026thinsp;11.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.508\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation. taVNS, transcutaneous auricular vagus nerve stimulation; ERP, event-related potential.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eVerification of effectiveness of taVNS\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents taVNS\u0026rsquo;s effect on performance and ERP P300 during AM task repetitions. The general linear mixed model demonstrated a main effect of taVNS on response time in the AM task (\u003cem\u003eβ\u003c/em\u003e: -545.755, 95% confidence interval (CI): -1002.736 to -88.775, p\u0026thinsp;=\u0026thinsp;0.018), highlighting that taVNS effectively reduced response time in the AM task compared to the sham task. ERP P300 exhibited a main effect of taVNS on Fz (\u003cem\u003eβ\u003c/em\u003e: 26.215, 95% CI: 13.762 to 38.667, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), Cz (\u003cem\u003eβ\u003c/em\u003e: 28.059, 95% CI: 13.823 to 42.295, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and Pz (\u003cem\u003eβ\u003c/em\u003e: 31.981, 95% CI: 16.173 to 47.789, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), indicating that ERP P300\u0026rsquo;s peak amplitude increased with AM task repetition in the taVNS group compared to the sham group.\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\u003eVerification of effectiveness of taVNS\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\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=\"char\" char=\".\" 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\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eβ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eβ SE\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e95%\u0026nbsp;CI\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eWald\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003ep\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAM performance: number of correct responses\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e7.660\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.567\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-1.292 to 16.612\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.812\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.094\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.286\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.794\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-4.192 to 6.764\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.212\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.645\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation*time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.286\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.767\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-2.179 to 4.750\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.529\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.467\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAM performance: response time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-545.755\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e230.497\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-1002.736 to -88.775\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e5.606\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.018\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-273.236\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e141.0416\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-552.863 to 6.391\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e3.753\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.053\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation*time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e83.404\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e89.202\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-93.448 to 260.255\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.874\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.350\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eERP P300: Fz\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e26.215\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e6.353\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.762 to 38.667\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e17.025\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.273\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.887\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-4.346 to 10.893\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.709\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.400\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation*time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-2.190\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.458\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-7.009 to 2.629\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.793\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.373\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eERP P300: Cz\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e28.059\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e7.263\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e13.823 to 42.295\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e14.924\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e3.346\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.444\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-5.365 to 12.057\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.567\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.452\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation*time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-1.791\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e2.810\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-7.301 to 3.718\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.406\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.524\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eERP P300: Pz\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e31.981\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8.065\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e16.173 to 47.789\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e15.723\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTime\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e6.274\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.935\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-3.399 to 15.947\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.616\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.204\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eStimulation*time\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e-3.498\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.316\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-9.161 to 2.620\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e1.256\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.262\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eStimulation (1: transcutaneous auricular vagus nerve stimulation; 2: sham). Time (1: Time 1; 2: Time 2; 3: Time 3). 95% CI, 95% confidence interval; AM, associative memory; ERP, event-related potential.\u003c/p\u003e\u003cp\u003e\u003cb\u003eChanges in salivary amylase\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e4\u003c/span\u003e displays the absence of changes in salivary amylase levels before and after stimulation.\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 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eChanges in salivary amylase\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ePre\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePost\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ep\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eTranscutaneous auricular vagus nerve stimulation\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e38.6\u0026thinsp;\u0026plusmn;\u0026thinsp;42.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e47.3\u0026thinsp;\u0026plusmn;\u0026thinsp;52.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.214\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSham\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e53.0\u0026thinsp;\u0026plusmn;\u0026thinsp;42.8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e50.0\u0026thinsp;\u0026plusmn;\u0026thinsp;34.5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e0.594\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSingle-blind validation\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e5\u003c/span\u003e summarizes each participant\u0026rsquo;s subjective ratings of stimulus type at the end of the experiment. The chi-squared analysis revealed no statistically significant differences, suggesting the integrity of the single-blind design.\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 5\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSingle-blind validation: chi-square test\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=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"2\" morerows=\"1\" nameend=\"c2\" namest=\"c1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003eStimulation type\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003ep\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003etaVNS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSham\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eSubjective stimulation type\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003etaVNS\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003e0.440\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSham\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003etaVNS: Transcutaneous auricular vagus nerve stimulation\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis crossover, single-blind, active versus sham experiment demonstrated that taVNS increased the ERP P300 peak amplitude and reduced the response time during the AM task compared to the sham using a general linear mixed model. Therefore, we speculate that taVNS secreted NE in neocortical regions and enhanced AM task performance.\u003c/p\u003e\u003cp\u003eThe ERP P300 peak amplitude is sensitive to the noradrenergic system and is considered an indicator of LC-NE activation (Brown et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Badran et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Burger et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Furthermore, it is also used as evidence that taVNS enhances cognitive aspects such as memory, attention, and cognitive inhibition (Fischer et al. 2017; Warren et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Burger et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). This is explained by the LC-P300 theory, which states that NE secreted from the LC activates the entire neocortex (Nieuwenhuis et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Several studies reported increases in the P300 peak amplitude and cognitive performance with taVNS (Fischer et al. 2017; Gurtubay et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Giraudier et al, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2024\u003c/span\u003e); nonetheless, they were limited to measuring P300 in only one region. Interestingly, we measured the Fz, Cz, and Pz regions along the neocortex and found an increase in P300 peak amplitude in these regions, providing evidence for a relationship between taVNS and the LC-P300 theory.\u003c/p\u003e\u003cp\u003eThis study demonstrated the effect of taVNS on response time reduction during AM tasks. The LC-P300 theory is based on the NE activation within the frontoparietal attention network (Nieuwenhuis et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Importantly, our findings corroborate those of previous studies that reported improved response times in various cognitive tasks (Nieuwenhuis et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Rufener et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wienke et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The lack of change in the number of correct responses observed in our study suggests that taVNS may enhance attentional function rather than memory (Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Kaan et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Naparstek 2023). Kaan et al. examined taVNS\u0026rsquo;s effects on verbal memory demonstrating improved performance over sham only in tasks with high demands for attention and inhibition (Kaan et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, Zhao et al. showed that taVNS improved working memory performance in sleep-deprived subjects; nevertheless, this may have resulted from increased arousal (Zhao et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Here, the fact that taVNS did not improve the number of correct responses while reducing response time may be due to enhanced attentional function rather than enhanced memory.\u003c/p\u003e\u003cp\u003eHowever, substantial research reported that taVNS enhances memory performance in older adults with mild cognitive impairment and epilepsy (Jacobs et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Pan et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Szeska et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; An et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Specifically, Jacobs et al.\u0026rsquo;s single-arm study reported an increased number of correct responses in an AM task following taVNS in older adults (Jacobs et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This may be explained by the fact that subjects with cognitive decline may be more likely to benefit from taVNS owing to sympathetic dominance and decreased NE secretion (Broncel et al, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Naparstek et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Additionally, the healthy adults in this study may have exhibited a ceiling effect on the memory task because their cognitive functions were intact (Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Naparstek 2023; An et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Previously, we observed a ceiling effect when an AM task was repeated (Sun et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Therefore, the effects of taVNS on memory tasks warrant further investigation.\u003c/p\u003e\u003cp\u003eThis study was conducted with a constant stimulus intensity (0.5 mV) for all subjects based on previous research; this differs from threshold method used in many other studies to set the stimulus intensity (Beste et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Colzato et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mertens et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Our stimulus intensity may have been weaker for some participants compared with that of the threshold method. Here, taVNS\u0026rsquo;s effect was confirmed by general linear mixed effects with individuals as random effects, indicating that some subjects may have not benefited from taVNS. Nonetheless, no adverse events typically identified in taVNS studies, such as prickling, were reported by our participants, supporting safe and effective taVNS. Further experiments to determine optimal taVNS settings are warranted.\u003c/p\u003e\u003cp\u003e\u003cb\u003eLimitations\u003c/b\u003e\u003c/p\u003e\u003cp\u003eThis study had some limitations. First, the carryover effect, which is often present in crossover designs, should be taken into account. Nevertheless, AM performance and peak amplitude of ERP at Time 1 did not differ significantly between groups. Furthermore, recent studies have shown that taVNS may not exhibit a carryover effect over time (Miyatsu et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Second, the absence of a main effect of taVNS on the number of correct responses may be related to the floor-ceiling effect of the task. Finally, salivary amylase levels may be an inappropriate surrogate marker of NE; recent studies recommend P300 or pupil diameter as a measure of NE changes (Villani et al. \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Wienke et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study examined the effects of taVNS on AM performance and ERP P300. This study indicated that taVNS increased the P300 peak amplitude at Fz, Cz, and Pz in the neocortex and reduced response time in the AM task. Our results provide data to support the effect of taVNS on AM. Because neuromodulation is noninvasive and simple, its application in the rehabilitation of cognitive function is desirable. For clinical applications, the effects of taVNS on cognitive function and optimal application methods should be continuously investigated.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by JSPS KAKENHI Grant-in-Aid for Early-Career Scientists Number 24K20544.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization: H.A; Methodology: H.A; Formal analysis and investigation: H.A, M.S, and T.H; Writing - original draft preparation: H.A; Writing - review and editing: H.A, M,S, T.H, and T.N; Funding acquisition: H.A; Resources: H.A; Supervision: H.A.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in accordance with the Declaration of Helsinki, and its protocol was approved by the Institutional Review Board of Niigata University of Health and Welfare (No. 19433-241111).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed consent\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll participants provided written informed consent prior to participation in the experiment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData from this experiment can be found in Appendix 1.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAn, S., Oh, S. J., Noh, S., Jun, S. B., Sung, J. E (2025) Enhancing cognitive abilities through transcutaneous auricular vagus nerve stimulation: Findings from prefrontal functional connectivity analysis and virtual brain simulation. NeuroImage 311:121179. https://doi.org/10.1016/j.neuroimage.2025.121179\u003c/li\u003e\n\u003cli\u003eAniwattanapong, D., List, J. J., Ramakrishnan, N., Bhatti, G. S., Jorge, R (2022) Effect of Vagus Nerve Stimulation on Attention and Working Memory in Neuropsychiatric Disorders: A Systematic Review. Neuromodulation : journal of the International Neuromodulation Society 25:343\u0026ndash;355. https://doi.org/10.1016/j.neurom.2021.11.009\u003c/li\u003e\n\u003cli\u003eAwh, E., Vogel, E. K., Oh, S. H (2006) Interactions between attention and working memory. Neuroscience 139:201\u0026ndash;208. https://doi.org/10.1016/j.neuroscience.2005.08.023\u003c/li\u003e\n\u003cli\u003eBadran, B. W., Dowdle, L. T., Mithoefer, O. 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International journal of clinical and health psychology : IJCHP 24:100462. https://doi.org/10.1016/j.ijchp.2024.100462\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"Transcutaneous auricular vagus nerve stimulation, associative memory, event-related potential, rehabilitation","lastPublishedDoi":"10.21203/rs.3.rs-7263208/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7263208/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTranscutaneous auricular vagus nerve stimulation (taVNS) is attracting attention as a new neuromodulation to improve cognitive function. The effects of this neuromodulation on associative memory and its mechanisms have not been fully investigated. This crossover, single-blind, active-versus-sham design experiment examined the effects of taVNS on associative memory performance and event-related potential P300, a biomarker of norepinephrine. The experiment consisted of an associative memory task with encoding and retrieval as a set, performed three times with a 10 min rest period, on 14 healthy adults. Participants received taVNS or sham during the 10 min rest between the time 1 and time 2. Event-related potentials were measured at each time of the associative memory task. The washout for this experiment was set at one week. We analyzed the effects of taVNS by means of a general linear mixed model with performance on three associative memory tasks and peak amplitude of event-related potential P300 as dependent variables. The results presented a main effect of taVNS on response time in an associative memory task. We also found a main effect of taVNS on the peak amplitude of event-related potential P300 at Fz, Cz, and Pz. This study indicated that when NE secretion is promoted by taVNS, associative memory performance is enhanced. This noninvasive neuromodulation has potential applications in rehabilitation for cognitive function and should be further investigated for application.\u003c/p\u003e\u003cp\u003e\u003cb\u003eRegistration\u003c/b\u003e: University Hospital Medical Information Network Center (No. UMIN000055911), date: January 24, 2024 \u0026ldquo;retrospectively registered\u0026rdquo;.\u003c/p\u003e","manuscriptTitle":"Effects of transcutaneous auricular vagus nerve stimulation on associative memory and event-related potential P300: a single-blind experiment on healthy adults","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-08 16:11:34","doi":"10.21203/rs.3.rs-7263208/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":"9e15c3b7-a707-4038-83e8-76c429c727d2","owner":[],"postedDate":"August 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-10-06T16:12:02+00:00","versionOfRecord":{"articleIdentity":"rs-7263208","link":"https://doi.org/10.1007/s00221-025-07171-z","journal":{"identity":"experimental-brain-research","isVorOnly":false,"title":"Experimental Brain Research"},"publishedOn":"2025-10-05 15:58:03","publishedOnDateReadable":"October 5th, 2025"},"versionCreatedAt":"2025-08-08 16:11:34","video":"","vorDoi":"10.1007/s00221-025-07171-z","vorDoiUrl":"https://doi.org/10.1007/s00221-025-07171-z","workflowStages":[]},"version":"v1","identity":"rs-7263208","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7263208","identity":"rs-7263208","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}