{"paper_id":"36198aaa-177d-4486-aa0a-b5adc9e855d1","body_text":"Cortical Spectral Dynamics of Vibrotactile Frequency Processing | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Cortical Spectral Dynamics of Vibrotactile Frequency Processing Nabi Rustamov, Phillip Demarest, Zhuangyu Han, Safia Mohamud, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6043161/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract While scientific research has extensively explored how the brain integrates touch and pain signals, the cerebral processing of specific vibrotactile frequencies remains poorly understood. This gap is particularly significant given clinical evidence that vibrotactile stimulation can reduce pain in both chronic pain patients and experimental settings. Our study investigated the cortical electrophysiological correlates of peripheral vibrotactile stimulation across different frequencies in healthy volunteers, with a focus on frequency-dependent patterns of neuronal activation. While electroencephalogram (EEG) was recorded, healthy participants received vibrotactile stimulation to the left index fingertip at frequencies corresponding to established neural rhythms: delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz). We compared the EEG bandwidth activity between vibrotactile stimulation conditions relative to resting baseline. Our findings demonstrated that vibrotactile stimulation produces distinct frequency-dependent patterns of cortical activation. A key finding was that 6 Hz stimulation selectively enhanced theta power in the left prefrontal cortex - an electrophysiological signature previously linked to successful pain relief. These findings advance the understanding of the \"spectrotopic\" nature of vibrotactile frequency processing in the cortex and provide a mechanistic foundation for developing novel vibration-based therapies in the future. Biological sciences/Neuroscience Biological sciences/Physiology Vibrotactile Stimulation Power Spectra Frontal Theta Power Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction While scientific research has extensively explored how the brain integrates touch and pain signals 1 – 4 , the understanding of how the brain processes specific frequencies of vibrotactile (vibrating touch) stimulation remains limited. This gap in knowledge is particularly important given the clinical evidence that vibrotactile stimulation can significantly reduce pain in both chronic pain patients and experimental settings, an effect that occurs independently of distraction 5 – 10 . The analgesic benefits may stem from vibrotactile stimuli restoring the balance between painful and non-painful sensory inputs, thereby normalizing pain perception 11 . At the physiological level, vibrotactile information is initially processed in the periphery by two types of sensory receptors: Meissner corpuscles, which respond better to lower frequencies, and Pacinian corpuscles, which are more sensitive to higher frequencies 12 . This frequency-specific processing likely extends to the cortical level, though through different mechanisms. Neuroimaging studies have revealed that vibrotactile perception activates a widespread cortical network, including primary (S1) and secondary (S2) somatosensory cortices, with activation patterns that vary depending on the vibration frequency 13 – 16 . However, electrophysiological evidence for these frequency-dependent effects remains scarce. Cortical neurons show stimulus-specific activity patterns in response to various vibrotactile inputs 17 , 18 , yet a comprehensive understanding of how the brain processes the full range of vibrotactile frequencies remains elusive. Moreover, the large-scale neuronal processing mechanisms underlying the analgesic effects of tactile somatosensory stimulation remain largely unknown. This study investigated the cortical electrophysiological correlates of peripheral vibrotactile stimulation across different frequencies in healthy volunteers, with a particular focus on frequency-dependent patterns of neuronal activation. Recent studies have demonstrated the association between pain relief and theta power enhancement in the left lateral frontal lobe 19 , 20 . In a separate study, a vibrotactile BCI (Brain-Computer Interface) neurofeedback system was used to enhance left frontal theta power in patients with chronic upper extremity pain 21 . The 6-week vibrotactile BCI therapy resulted in reductions in both pain severity and pain interference scores, which were positively correlated with the magnitude of the frontal theta power increase. This effect was specific to theta rhythms and was not observed in any other power bands, emphasizing the unique role of frontal theta power increase in pain relief. Further refinement of the vibration parameters to improve analgesia, however, requires an improved understanding of the cortical processing of vibrotactile stimuli. While electroencephalogram (EEG) was recorded, healthy participants received vibrotactile stimulation to the left index fingertip at frequencies corresponding to established neural rhythms: delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz). The results showed frequency-specific cortical topographic activations. Interestingly, 6 Hz stimulation effectively enhanced ipsilateral theta power over the left frontal area. These findings advance the understanding of the “spectrotopic” nature of vibrotactile frequency processing in the cortex and may be relevant to future vibrotactile therapeutic strategies for pain. Results Participant Demographics and Clinical Characteristics A total of 20 participants completed the study, comprising 9 females and 11 males. The mean age was 32.8 ± 7.2 years (age range: 23-45 years). As planned, the stimulation voltage was individually calibrated using a staircase method to induce a significant vibration sensation (rating of 7 on the NRS) in all participants. On average, participants reported pain catastrophizing scale score of 10.7 ± 4.2, depression score of 2.2 ± 1.6 and anxiety score of 4.2 ± 1.4, indicating the absence of clinically significant pain catastrophizing, anxiety or depression. EEG Effects Modulation of Resting Baseline Power by Vibrotactile Stimulation The EEG bandwidth activity was compared between vibrotactile stimulation conditions and resting baseline as measured over the electrode sites ( Figs. 1 and 3 , event-related spectral perturbations; Figs. 2 and 4 , topographic patterns). 2 Hz Stimulation: theta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps < 0.05, maximum effect at C4 electrode, t = 2.9) ( Figs. 1 and 2, left panels ). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4, P4 and C3 electrodes, all Ps < 0.05, maximum effect at P4 electrode, t = 4.6). Delta, beta, low- and high- gamma frequency bands did not show significant changes. 6 Hz Stimulation: theta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps < 0.05, maximum effect at C4 electrode, t = 4.8) ( Figs. 1 and 2, middle panels ). Moreover, there was theta power enhancement over the frontal area with lateralization to the ipsilateral hemisphere (significant effects at the F3 and Fz electrodes, both Ps < 0.05, maximum effect at F3 electrode, t = 4.9). Alpha frequency bands showed power decreases over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, all Ps < 0.05, maximum effect at C4 electrode, t = 3.0). Delta, beta, low- and high- gamma frequency bands did not show significant changes. 12 Hz Stimulation: theta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps < 0.05, maximum effect at C4 electrode, t = 3.0) ( Figs. 1 and 2, right panels ). A nonsignificant trend emerged for theta power increase at the F3 and Fz electrodes (both Ps > 0.05). Alpha frequency bands showed power decreases over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, all Ps < 0.05, maximum effect at C4 electrode, t = 4.7). Delta, beta, low- and high- gamma frequency bands did not show significant changes. 20 Hz Stimulation: theta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps < 0.05, maximum effect at C4 electrode, t = 3.2) ( Figs. 3 and 4, left panels ). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4 and C3 electrodes, all Ps < 0.05, maximum effect at C3 electrode, t = 3.3). Delta, beta, low- and high- gamma frequency bands did not show significant changes. 40 Hz Stimulation: theta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps < 0.05, maximum effect at P4 electrode, t = 3.1) ( Figs. 3 and 4, right panels ). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4, P4 and C3 electrodes, all Ps < 0.05, maximum effect at C4 electrode, t = 3.4). Delta, beta, low- and high- gamma frequency bands did not show significant changes. ----- Figures 1, 2, 3, 4 approximately here ----- Comparison of Power Modulations Induced by Vibrotactile Stimulation Figures 5 and 6 show the mean power values across five patterns of vibrotactile stimulation (2 Hz, 6 Hz, 12 Hz, 20 Hz and 40 Hz stimulation) relative to resting baseline. The power was examined in an ANOVA with within-subject’s factors Stimulation (1) - (5) × Electrode (1) - (7). In case of significant interaction Stimulation × Electrode, indicating an overall difference between vibrotactile stimulation conditions with regard to the power as a function of the electrode, we ran separate ANOVAs for each electrode (see the “Statistical Analyses” section). Delta band. The main effect of the stimulation, F(6,456) = 1.7, P = 0.14, did not prove significant, but interaction Stimulation × Electrode, F(6,456) = 2.4, P < 0.001, was significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode ( Fig. 5, left panels ). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 8.0, P < 0.001, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in delta power at the Fz electrode in response to 40 Hz stimulation compared to 2 Hz (P < 0.04), 6 Hz (P < 0.03) and 12 Hz (P < 0.02) stimulation. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 10.0, P < 0.001, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a similar pattern of delta power decrease at the F3 electrode induced by 40 Hz stimulation as compared to stimulation at 6 Hz (P < 0.005) and 12 Hz (P < 0.002). At the F4 electrode, the main effect of the stimulation proved significant, F(4,76) = 3.2, P < 0.02, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in delta power at the F4 electrode in response to 40 Hz stimulation compared to 6 Hz (P < 0.02) stimulation. The C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 1.0, 2.3, 0.7 and 0.9, and P = 0.42, 0.07, 0.61 and 0.48, respectively, indicating that delta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 40 Hz stimulation inhibited delta power over the frontal areas. Theta band. The main effect of the stimulation, F(6,456) = 30.7, P < 0.001, and interaction Stimulation × Electrode, F(6,456) = 7.6, P < 0.001, were significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode ( Fig. 5, middle panels ). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 13.4, P < 0.001, indicating that theta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant increase in theta power at the Fz electrode in response to 6 Hz stimulation compared to 2 Hz (P < 0.003), 12 Hz (P < 0.004), 20 Hz (P < 0.001) and 40 Hz (P < 0.001) stimulation. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 30.2, P < 0.001, indicating that theta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a similar pattern of theta power increase at the F3 electrode induced by 6 Hz stimulation as compared to stimulation at 2 Hz (P < 0.001), 12 Hz (P < 0.001), 20 Hz (P < 0.001) and 40 Hz (P < 0.001). The F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.0, 1.2, 2.1, 0.9 and 0.3, and P = 0.10, 0.31, 0.09, 0.48 and 0.9, respectively, indicating that theta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 6 Hz stimulation was effective in inducing frontal theta power enhancement over the central frontal and left frontal areas. Alpha band. The main effect of the stimulation, F(6,456) = 21.4, P < 0.001, and interaction Stimulation × Electrode, F(6,456) = 2.3, P < 0.001, were significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode ( Fig. 5, right panels ). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 2.5, P < 0.05, indicating that alpha power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in alpha power at the Fz electrode in response to 40 Hz stimulation compared to 6 Hz stimulation (P < 0.02). At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 5.7, P < 0.001, indicating that alpha power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed alpha power decrease at the F3 electrode induced by 20 Hz stimulation as compared to stimulation at 6 Hz (P < 0.003) and 12 Hz (P < 0.02). The F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.2, 1.6, 1.7, 0.2 and 0.3, and P = 0.08, 0.19, 0.15, 0.92 and 0.88, respectively, indicating that alpha power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 20 Hz and 40 Hz stimulations inhibited frontal alpha power over the left frontal and central frontal areas, respectively. Beta band. The main effect of the stimulation, F(6,456) = 0.6, P = 0.72, did not prove significant, but interaction Stimulation × Electrode, F(6,456) = 2.2, P < 0.002, was significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode ( Fig. 6, left panels ). We conducted separate ANOVAs for each electrode. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 3.7, P < 0.009, indicating that beta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant increase in beta power at the F3 electrode in response to 6 Hz stimulation compared to 12 Hz stimulation (P < 0.02). The Fz, F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.2, 2.3, 0.6, 0.7, 2.0 and 2.1, and P = 0.08, 0.07, 0.67, 0.24, 0.10 and 0.09, respectively, indicating that beta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 6 Hz stimulation induced frontal beta power over the left frontal area. Low-gamma band. The main effect of the stimulation, F(6,456) = 1.4, P = 0.23, and interaction Stimulation × Electrode, F(6,456) = 0.9, P = 0.60, did not prove significant, indicating that low-gamma power was not significantly modulated with the use of a vibrotactile stimulation ( Fig. 6, middle panels ). High-gamma band. The main effect of the stimulation, F(6,456) = 0.7, P = 0.61, and interaction Stimulation × Electrode, F(6,456) = 0.8, P = 0.63, did not prove significant, indicating that high-gamma power was not significantly modulated with the use of a vibrotactile stimulation ( Fig. 6, right panels ). ----- Figures 5, 6 approximately here ----- Discussion Although vibrotactile stimulation has demonstrated therapeutic potential, the cortical mechanisms underlying frequency-specific somatosensory processing remain poorly characterized. This study revealed that different vibration frequencies produce distinct patterns of cortical spectral modulation, suggesting a \"spectrotopic\" organization of vibrotactile processing. Of particular clinical relevance, 6 Hz stimulation uniquely enhanced theta power in the left frontal region - an electrophysiological signature previously associated with successful pain relief in both chronic pain patients and experimental settings. These findings advance our fundamental understanding of how the brain processes tactile frequency information and suggest potential mechanistic pathways by which vibrotactile stimulation may modulate pain perception. Among the tested frequencies, only 6 Hz stimulation significantly increased frontal theta power, while 2 Hz and 12 Hz showed minor, non-significant increases. Higher frequencies (20 Hz and 40 Hz) produced slight, non-significant decreases in frontal theta power. These distinct responses suggest frequency-specific theta rhythm dynamics in the frontal cortex during distinct frequencies of vibrotactile stimulation. The most pronounced effect was enhanced synchronization of theta oscillations over frontal areas involving F3 electrode during 6 Hz stimulation, corresponding to the left prefrontal cortex 22 , 23 . Neuromodulation studies suggest that increased activity in the prefrontal cortical areas plays a crucial role in pain management 24 , 25 . The prefrontal cortex is involved in cognitive and regulatory functions, and through its connections to different functional brain networks, plays a role in cognitive and emotional control over pain 26 , 27 . From an electrophysiological standpoint, successful pain relief, both in chronic pain patients and in the context of experimental pain relief, was found to be associated with an increase in the left prefrontal theta activity 19 , 20 . A previous study demonstrated the effectiveness of frontal theta reinforcement in patients with chronic upper extremity pain using a vibrotactile BCI neurofeedback system, which resulted in reductions in both pain severity and pain interference scores 21 . During vibrotactile BCI therapy, the magnitude of frontal theta power increase at F3 electrode positively correlated with pain relief. This specificity to theta rhythms, absent in other frequency bands, underscores its unique role in pain reduction. Thus, an increase in frontal theta power may contribute to the analgesic effects of vibration stimulation, but further research is needed to elucidate the neural circuits underlying these effects. Our study replicated several established patterns of cortical activity during tactile stimulation. Vibrotactile stimulation induced a significant decrease in alpha power over the central area compared to the resting state. The latter is referred to as alpha-event-related desynchronization (ERD), a well-known phenomenon during both non-nociceptive and nociceptive stimulation, likely related to nonspecific arousal and attention to stimuli 2 , 3 , 28 . It can be inferred that vibrotactile stimulation enhances the excitability of sensorimotor cortical neurons, leading to a decrease in alpha power, which is consistent with previous studies 15 , 29 , 30 . Numerous imaging studies have shown that desynchronized alpha power emerges concurrently with increased activity in the sensorimotor cortex during motor tasks 31 , 32 . Thus, alpha suppression is unlikely to be a phenomenon specific to pure somatosensation. Vibration stimulation also resulted in an increase in theta power over the central area compared to the resting state. Theta oscillations are recognized for their involvement in attentional processes 33 . Therefore, the increased theta power in the sensorimotor cortex likely reflects heightened attention to the sensory stimulation, as the brain processes both visual and tactile inputs. This event-related synchronization (ERS) of theta rhythms showed a lateralized pattern, with stronger activation in the somatosensory area opposite to the stimulated hand - a pattern consistent with the brain's contralateral processing of sensory information. These findings are consistent with known bilateral cortical representation of somatosensation with lateralization to the contralateral somatosensory cortex 34 . Notably, theta power modulation in the sensorimotor area may be associated with both tactile and painful stimulation 2 , 28 , 35 – 37 . Thus, these findings are not likely to be specific to vibrotactile stimulation. This study has the following limitations. Our sample size was limited to 20 participants. While vibrotactile stimulation serves as a useful model for studying the underlying brain mechanisms of frequency processing and developing novel treatment approaches, our results should be tested in patients with chronic pain before drawing broader conclusions. In conclusion, our findings demonstrated that vibrotactile stimulation produces distinct frequency-dependent patterns of cortical activation, advancing our understanding of how the brain processes tactile frequency information. A key finding was that 6 Hz stimulation of the left index finger selectively enhanced theta power in the left prefrontal cortex - an electrophysiological signature previously linked to successful pain reduction in both clinical and experimental settings. These results provide a mechanistic foundation for developing novel vibration-based therapies in the future. Materials and Methods Ethical Approval This study was approved by the institutional review board of Washington University School of Medicine in St. Louis. All experimental procedures conformed to the standards set by the latest revision of the Declaration of Helsinki. All participants provided written informed consent before participation in the study. Participants This was a study with a single group consisting of 20 healthy participants. Healthy participants for the experiment were recruited through advertising the study via ads posting flyers at Washington University School of Medicine in St. Louis. Willing participants have been screened for inclusion and exclusion criteria. Inclusion criteria for the study were healthy male or female participants of any age between 18 and 50 years, with no major conditions of any organ system. Participants were excluded if they had any history of acute or chronic pain condition including episodic primary headaches, acute or chronic illness, or a diagnosed psychiatric disorder. To avoid any confounding by recent administration of pain medications, participants did not take any analgesics including non-steroidal anti-inflammatory drugs (NSAIDs) or acetaminophen for at least five drug half-lives prior to any study visit. Participants did not use caffeinated products for 3 h before the study as these can also affect electroencephalographic recording 38 . After screening and obtaining written informed consent, participants were asked to provide basic demographic information and to complete the Pain Catastrophizing Scale, Beck Depression Inventory and Beck Anxiety Inventory questionnaires 39-41 . Experimental Paradigm The study took place in a quiet study room with minimal outside disturbance. During the calibration phase, the vibrotactile stimulus intensity required to elicit a rating of 7 on a 0–10 Numerical Rating Scale (NRS) was determined, where 0 = no sensation, 3 = first instance of tactile sensation, 5 = moderate tactile sensation, 7 = significant tactile sensation, and 10 = first instance of pain. The stimulation voltage was individually calibrated using a staircase method, involving incremental increases and decreases in intensity (ranging from 10 to 30 V), applied to the left index fingertip until a rating of 7 on the NRS was reached three times. These parameters were subsequently used during the experimental phase. During this phase, participants were seated comfortably in a chair and instructed to minimize their movements during EEG data collection. Throughout the experiment, the participants were instructed to fixate on a fixation cross presented centrally on the screen to avoid excessive eye blinking while keeping their eyes open. Brain activity was recorded by means of EEG during two consecutive states: resting baseline and vibrotactile stimulation ( Fig. 7 ). Resting baseline: baseline EEG was recorded for 5 minutes during which participants were instructed not to perform any mental activity or have any specific thoughts but to remain calm and relaxed as much as possible, while not falling asleep. Vibrotactile stimulation: vibrotactile stimuli were delivered to the tip of the left index finger using five different types of stimuli corresponding to delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz) frequencies, with 20 trials conducted for each frequency. Because neural activities can be modulated by attention during the stimulus presentation 42,43 , the participants were asked to pay attention to all stimuli. The stimulation voltage was individually calibrated to induce significant tactile sensation (refer to the calibration phase described earlier in this paragraph). The stimulus duration of each trial was 5 sec, with an inter-stimulus interval of 5, 6, or 7 sec, and all trials and inter-stimulus intervals were randomized. ----- Figure 7 approximately here ----- Electroencephalogram Recording and Processing Electroencephalogram (EEG) was recorded by means of 24 wireless dry electrodes mounted on the EEG headset in an International 10–20 System (DSI 24, Wearable Sensing, San Diego, CA, USA). EEG was referenced to the Pz electrode, sampled at 600 Hz with a ground electrode placed on the forehead. Electrode impedance was kept below 10 kΩ. The raw EEG data were preprocessed in MATLAB environment (Mathworks, Nattick, MA, USA). Continuous EEG recording was band-pass filtered between 1 and 100 Hz using a finite impulse response (FIR) filter. To remove environmental noise, 60 Hz notch filter was applied. EEG data were screened for extreme values, as well as for infrequent and unstereotyped artifacts. For further artifact attenuation, Infomax independent component analysis (ICA) was applied 44,45 . Independent components found to reflect eye blinks, lateral eye movements, muscle-related and cardiac artifacts were removed from the data. EEG data were common average re-referenced. Frequency bands were defined as follows: delta, 1–3 Hz; theta, 4–7 Hz; alpha, 8–13 Hz; beta, 14– 29 Hz; low-gamma, 30–58 Hz; high-gamma, 62–100 Hz 1,46 . Time-frequency analysis Time-frequency analysis was performed in MATLAB environment (Mathworks, Nattick, MA, USA) 3 . The EEG data were segmented into stimulus-locked epochs from −1,000 to 7,000 msec, with time 0 corresponding to the onset of vibrotactile stimulation. A Morlet wavelet convolution was computed. Two hundred time points were generated, and 100 linearly spaced frequencies were computed from 1 to 100 Hz. Variable cycles were used for low and high frequencies, with 3 cycles for lowest frequencies and up to 15 cycles for highest frequencies. This variable cycle allows the wavelet convolution method to provide a better frequency resolution at lower frequencies and a better temporal resolution at higher frequencies. Event-related spectral perturbations (ERSP) 47,48 were computed in decibels relative to the resting baseline. Specific frequency bands were defined as follows: delta (1-3 Hz) theta (4-7 Hz), alpha (8-12 Hz), beta (13-29 Hz), low-gamma (30-59 Hz) and high-gamma (62-100 Hz) 1,3 . The ERSP value for each time-frequency point was calculated for each participant. Topographic patterns of brain activity were illustrated for a value representing the mean activity at each frequency band. For each participant, the time-frequency data were averaged across all trials per condition. The grand average time-frequency maps were obtained by averaging data across all participants for each condition. Statistical Analyses We used non-parametric statistical inference to compare the EEG bandwidth activity between vibrotactile stimulation conditions and resting baseline that does not make assumptions on the distributions of the data 49-51 . Permutation tests were performed across participants for random effects inference. All statistical tests were two-tailed with a significance level of 0.05. Under the null hypothesis of no difference in the EEG data between the vibrotactile stimulation and resting baseline, the electrode labels for each participant were randomly permuted between conditions and the resulting data were used to compute a permutation t-statistic spatiotemporal electrode map for the power. Repeating this permutation procedure 1,000 times, using Monte Carlo random sampling, enabled us to estimate the empirical distribution of the t-statistic at each electrode, and thus convert the original data into a p-value statistical map. Lastly, to control for multiple comparisons across all electrodes, the p-values were adjusted using a false discovery rate (FDR) procedure. The significant values with P ≤ 0.05 were retained while values with P > 0.05 were set to zero. Differences in the mean power values between vibrotactile stimulation conditions were examined in a repeated-measures ANOVA with within-subject’s factors Stimulation (main factor with five levels: 2 Hz, 6 Hz, 12 Hz, 20 Hz and 40 Hz vibrotactile stimulation - see the “Experimental Paradigm” section) × Electrode (F3, Fz, F4, C3, C4, P3 and P4). In case of significant interaction Stimulation × Electrode, indicating an overall difference between conditions with regard to the power as a function of the electrode, we ran separate ANOVAs for each electrode. Planned contrasts were then used to test a priori hypotheses and decompose the significant effects of vibrotactile stimulation. All statistical tests were two tailed with a significance level of 0.05, and the P-values were adjusted using an FDR correction. Declarations Acknowledgments The authors thank study participants for their time and effort. This study did not receive any funding. Author Contributions N.R. performed the experiment and data collection, performed the data analysis, and wrote the manuscript. P.D. aided in software development, and data collection. Z.H. aided in hardware development. S.M. wrote the manuscript. S.H. wrote the manuscript. E.C.L. oversaw engineering and electrophysiology-related implementation, supervised the project, and wrote the manuscript. All authors reviewed the manuscript. Data Availability The data will be made available upon reasonable request to the corresponding author. Disclosures ECL has stock ownership in Neurolutions, Inner Cosmos, Aurenar, and Sora Neuroscience. Washington University also owns stock in Neurolutions. This work and E.C. 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An inventory for measuring depression. Archives of general psychiatry 4 , 561-571, doi:10.1001/archpsyc.1961.01710120031004 (1961). Beck, A. T., Epstein, N., Brown, G. & Steer, R. A. An inventory for measuring clinical anxiety: psychometric properties. J Consult Clin Psychol 56 , 893-897, doi:10.1037//0022-006x.56.6.893 (1988). Osman, A. et al. Factor structure, reliability, and validity of the Pain Catastrophizing Scale. Journal of behavioral medicine 20 , 589-605, doi:10.1023/a:1025570508954 (1997). Steinmetz, P. N. et al. Attention modulates synchronized neuronal firing in primate somatosensory cortex. Nature 404 , 187-190, doi:10.1038/35004588 (2000). Ray, S., Niebur, E., Hsiao, S. S., Sinai, A. & Crone, N. E. High-frequency gamma activity (80-150Hz) is increased in human cortex during selective attention. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 119 , 116-133, doi:10.1016/j.clinph.2007.09.136 (2008). Rustamov, N. et al. Attention shifting in Parkinson's disease: an analysis of behavioral and cortical responses. Neuropsychology 28 , 929-944, doi:10.1037/neu0000099 (2014). Delorme, A. & Makeig, S. EEGLAB: an open source toolbox for analysis of single-trial EEG dynamics including independent component analysis. Journal of neuroscience methods 134 , 9-21, doi:10.1016/j.jneumeth.2003.10.009 (2004). Rustamov, N., Wagenaar-Tison, A., Doyer, E. & Piché, M. Electrophysiological investigation of the contribution of attention to altered pain inhibition processes in patients with irritable bowel syndrome. The journal of physiological sciences : JPS 70 , 46, doi:10.1186/s12576-020-00774-x (2020). Makeig, S. Auditory event-related dynamics of the EEG spectrum and effects of exposure to tones. Electroencephalography and clinical neurophysiology 86 , 283-293, doi:10.1016/0013-4694(93)90110-h (1993). Pfurtscheller, G. & Lopes da Silva, F. H. Event-related EEG/MEG synchronization and desynchronization: basic principles. Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology 110 , 1842-1857, doi:10.1016/s1388-2457(99)00141-8 (1999). Pantazis, D., Nichols, T. E., Baillet, S. & Leahy, R. M. A comparison of random field theory and permutation methods for the statistical analysis of MEG data. NeuroImage 25 , 383-394, doi:10.1016/j.neuroimage.2004.09.040 (2005). Maris, E. & Oostenveld, R. Nonparametric statistical testing of EEG- and MEG-data. Journal of neuroscience methods 164 , 177-190, doi:10.1016/j.jneumeth.2007.03.024 (2007). Rustamov, N., Humphries, J., Carter, A. & Leuthardt, E. C. Theta-gamma coupling as a cortical biomarker of brain-computer interface-mediated motor recovery in chronic stroke. Brain communications 4 , fcac136, doi:10.1093/braincomms/fcac136 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 13 May, 2025 Reviews received at journal 12 May, 2025 Reviewers agreed at journal 21 Apr, 2025 Reviews received at journal 03 Apr, 2025 Reviewers agreed at journal 24 Mar, 2025 Reviewers invited by journal 20 Mar, 2025 Editor assigned by journal 18 Mar, 2025 Editor invited by journal 20 Feb, 2025 Submission checks completed at journal 19 Feb, 2025 First submitted to journal 16 Feb, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-6043161\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":418766249,\"identity\":\"4da3c9f7-b2d8-4edd-a694-de07319751db\",\"order_by\":0,\"name\":\"Nabi Rustamov\",\"email\":\"data:image/png;base64,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\",\"orcid\":\"\",\"institution\":\"Washington University in St. Louis School of Medicine\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Nabi\",\"middleName\":\"\",\"lastName\":\"Rustamov\",\"suffix\":\"\"},{\"id\":418766250,\"identity\":\"bb7c822c-cf0d-4d81-847d-88cbe939688c\",\"order_by\":1,\"name\":\"Phillip Demarest\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Washington University in St. Louis School of Medicine\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Phillip\",\"middleName\":\"\",\"lastName\":\"Demarest\",\"suffix\":\"\"},{\"id\":418766251,\"identity\":\"42cbe554-1579-419f-91c0-6936f6f9c9b0\",\"order_by\":2,\"name\":\"Zhuangyu Han\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Washington University in St. Louis School of Medicine\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Zhuangyu\",\"middleName\":\"\",\"lastName\":\"Han\",\"suffix\":\"\"},{\"id\":418766252,\"identity\":\"8d95a3fc-5a05-4fae-9308-1261298b29bb\",\"order_by\":3,\"name\":\"Safia Mohamud\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Howard University Hospital, Howard University School of Medicine\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Safia\",\"middleName\":\"\",\"lastName\":\"Mohamud\",\"suffix\":\"\"},{\"id\":418766253,\"identity\":\"355f770b-7f84-4fbe-970f-f067b78e25bc\",\"order_by\":4,\"name\":\"Simon Haroutounian\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Washington University in St. Louis School of Medicine\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Simon\",\"middleName\":\"\",\"lastName\":\"Haroutounian\",\"suffix\":\"\"},{\"id\":418766254,\"identity\":\"7d91116f-deb9-4138-af16-cf017af23dac\",\"order_by\":5,\"name\":\"Eric C. Leuthardt\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Washington University in St. Louis School of Medicine\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Eric\",\"middleName\":\"C.\",\"lastName\":\"Leuthardt\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2025-02-16 21:53:15\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-6043161/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-6043161/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":76880708,\"identity\":\"fa59d54b-a629-4292-a397-d7b7338993cb\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:14\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":6020669,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eEvent-related spectral perturbations. \\u003c/strong\\u003eModulation of power spectra by vibrotactile stimulation at 2 Hz, 6 Hz, and 12 Hz relative to resting baseline. Mean stimulus-locked event-related spectral perturbations at the electrode level. Oscillatory power is presented in dB relative to a resting baseline. Positive and negative power changes are represented by red and blue colors, respectively. The mean power values for the frequency bands of interest (time × frequency) were calculated and statistical results were presented in the Results section. X-axis, time in sec; Y-axis, frequency in Hz. dB, decibel; Hz, hertz; HG, high-gamma; LG, low-gamma.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig1ERSP.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/babfa0eaa6945d06bc749a5c.png\"},{\"id\":76881640,\"identity\":\"5ef59817-14ec-4d3d-8992-f4c045994ab6\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:11:14\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":11358101,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eTopographic patterns of power spectra. \\u003c/strong\\u003ePower spectra were normalized relative to baseline (dB log power ratio). Positive and negative power changes are represented by red and blue colors, respectively. Electrode level tmaps of the comparison between conditions as assessed by nonparametric permutation tests. Only electrodes whose t statistic exceeded a critical threshold of P ≤ 0.05 (two-tailed, FDR corrected) were retained. For the electrodes not showing significant effects, t values were set to zero. Left column: 2 Hz stimulation. Middle column: 6 Hz stimulation. Right column: 12 Hz stimulation. dB, decibel; FDR, false discovery rate.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig2Topoplots.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/743f111b4b15ab9383745720.png\"},{\"id\":76880728,\"identity\":\"58f52f24-0034-48c3-8eab-68f371e6cfbd\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:19\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":3827229,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eEvent-related spectral perturbations. \\u003c/strong\\u003eModulation of power spectra by vibrotactile stimulation at 20 Hz and 40 Hz relative to resting baseline. Mean stimulus-locked event-related spectral perturbations at the electrode level. Oscillatory power is presented in dB relative to a resting baseline. Positive and negative power changes are represented by red and blue colors, respectively. The mean power values for the frequency bands of interest (time × frequency) were calculated and statistical results were presented in the Results section. X-axis, time in sec; Y-axis, frequency in Hz. dB, decibel; Hz, hertz; HG, high-gamma; LG, low-gamma.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig3ERSP.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/c80bbc5e29a6be416f120033.png\"},{\"id\":76880695,\"identity\":\"024f8fbf-67cf-4fdf-a02a-48edfd73ff58\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:14\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":7332168,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eTopographic patterns of power spectra. \\u003c/strong\\u003ePower spectra were normalized relative to baseline (dB log power ratio). Positive and negative power changes are represented by red and blue colors, respectively. Electrode level tmaps of the comparison between conditions as assessed by nonparametric permutation tests. Only electrodes whose t statistic exceeded a critical threshold of P ≤ 0.05 (two-tailed, FDR corrected) were retained. For the electrodes not showing significant effects, t values were set to zero. Left column: 20 Hz stimulation. Right column: 40 Hz stimulation. dB, decibel; FDR, false discovery rate.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig4Topoplots.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/96f8a64ddcda5f74f8de33f6.png\"},{\"id\":76880696,\"identity\":\"d2304b90-9ce7-49bb-be35-06d33311bfb3\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:14\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":2641923,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eMean power values.\\u003c/strong\\u003e Modulation of delta, theta, and alpha power by vibrotactile stimulation at different frequencies. Mean power values in dB for each electrode of interest. Y-axis, mean power value in dB; X-axis, vibrotactile stimulation conditions. Significance levels were based on the pairwise comparisons in ANOVA (N = 20; FDR corrected). *, ** and *** symbols: P ≤ 0.05, 0.01 and 0.001, respectively. dB, decibel; Hz, hertz.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig5MeanPower.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/6bc482716984200716c551a3.png\"},{\"id\":76880694,\"identity\":\"daaac9e3-498a-47b3-966b-5f43acfe8d05\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:13\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":1836420,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eMean power values.\\u003c/strong\\u003e Modulation of beta, low-gamma, and high-gamma power by vibrotactile stimulation at different frequencies. Mean power values in dB for each electrode of interest. Y-axis, mean power value in dB; X-axis, vibrotactile stimulation conditions. Significance levels were based on the pairwise comparisons in ANOVA (N = 20; FDR corrected). * symbol: P ≤ 0.05. dB, decibel; Hz, hertz.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig6MeanPower.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/111840b776e6d59f834934bb.png\"},{\"id\":76880705,\"identity\":\"5333c37c-4bd4-42a8-9184-a601d4dfd7c1\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:03:14\",\"extension\":\"png\",\"order_by\":7,\"title\":\"Figure 7\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":149409,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003e\\u003cstrong\\u003eExperimental Paradigm. \\u003c/strong\\u003eBrain activity was recorded by means of EEG during two consecutive states, resting baseline and vibrotactile stimulation. Resting baseline: baseline EEG was recorded for 5 minutes during which participants were instructed to remain calm and relaxed as much as possible. Vibrotactile stimulation: vibrotactile stimuli were delivered to the tip of the left index finger using five different types of stimuli corresponding to delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz) frequencies, with 20 trials conducted for each frequency. Unique vibrotactile stimulation conditions are depicted in different colors. The stimulus duration of each trial was 5 secs, with an inter-stimulus interval of 5, 6, or 7 sec, and all trials and inter-stimulus intervals were randomized. EEG, electroencephalogram; Hz, hertz; ISI, interstimulus interval.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Fig7ExperimentalParadigm.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/0d5295cd70f23250fd5acbc4.png\"},{\"id\":76882467,\"identity\":\"7082eb36-ffbe-48e2-aebe-2a082b4e31c9\",\"added_by\":\"auto\",\"created_at\":\"2025-02-21 17:27:25\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":30587613,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-6043161/v1/866be989-ff2b-4b05-8d15-afad138c90a6.pdf\"}],\"financialInterests\":\"No competing interests reported.\",\"formattedTitle\":\"Cortical Spectral Dynamics of Vibrotactile Frequency Processing\",\"fulltext\":[{\"header\":\"Introduction\",\"content\":\"\\u003cp\\u003eWhile scientific research has extensively explored how the brain integrates touch and pain signals \\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR2 CR3\\\" citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR4\\\" class=\\\"CitationRef\\\"\\u003e4\\u003c/span\\u003e\\u003c/sup\\u003e, the understanding of how the brain processes specific frequencies of vibrotactile (vibrating touch) stimulation remains limited. This gap in knowledge is particularly important given the clinical evidence that vibrotactile stimulation can significantly reduce pain in both chronic pain patients and experimental settings, an effect that occurs independently of distraction \\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR6 CR7 CR8 CR9\\\" citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e5\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e10\\u003c/span\\u003e\\u003c/sup\\u003e. The analgesic benefits may stem from vibrotactile stimuli restoring the balance between painful and non-painful sensory inputs, thereby normalizing pain perception \\u003csup\\u003e\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003e11\\u003c/span\\u003e\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003eAt the physiological level, vibrotactile information is initially processed in the periphery by two types of sensory receptors: Meissner corpuscles, which respond better to lower frequencies, and Pacinian corpuscles, which are more sensitive to higher frequencies \\u003csup\\u003e\\u003cspan citationid=\\\"CR12\\\" class=\\\"CitationRef\\\"\\u003e12\\u003c/span\\u003e\\u003c/sup\\u003e. This frequency-specific processing likely extends to the cortical level, though through different mechanisms. Neuroimaging studies have revealed that vibrotactile perception activates a widespread cortical network, including primary (S1) and secondary (S2) somatosensory cortices, with activation patterns that vary depending on the vibration frequency \\u003csup\\u003e\\u003cspan additionalcitationids=\\\"CR14 CR15\\\" citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e13\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e16\\u003c/span\\u003e\\u003c/sup\\u003e. However, electrophysiological evidence for these frequency-dependent effects remains scarce. Cortical neurons show stimulus-specific activity patterns in response to various vibrotactile inputs \\u003csup\\u003e\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e17\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e18\\u003c/span\\u003e\\u003c/sup\\u003e, yet a comprehensive understanding of how the brain processes the full range of vibrotactile frequencies remains elusive. Moreover, the large-scale neuronal processing mechanisms underlying the analgesic effects of tactile somatosensory stimulation remain largely unknown.\\u003c/p\\u003e \\u003cp\\u003eThis study investigated the cortical electrophysiological correlates of peripheral vibrotactile stimulation across different frequencies in healthy volunteers, with a particular focus on frequency-dependent patterns of neuronal activation. Recent studies have demonstrated the association between pain relief and theta power enhancement in the left lateral frontal lobe \\u003csup\\u003e\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e\\u003c/sup\\u003e. In a separate study, a vibrotactile BCI (Brain-Computer Interface) neurofeedback system was used to enhance left frontal theta power in patients with chronic upper extremity pain \\u003csup\\u003e\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e\\u003c/sup\\u003e. The 6-week vibrotactile BCI therapy resulted in reductions in both pain severity and pain interference scores, which were positively correlated with the magnitude of the frontal theta power increase. This effect was specific to theta rhythms and was not observed in any other power bands, emphasizing the unique role of frontal theta power increase in pain relief. Further refinement of the vibration parameters to improve analgesia, however, requires an improved understanding of the cortical processing of vibrotactile stimuli. While electroencephalogram (EEG) was recorded, healthy participants received vibrotactile stimulation to the left index fingertip at frequencies corresponding to established neural rhythms: delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz). The results showed frequency-specific cortical topographic activations. Interestingly, 6 Hz stimulation effectively enhanced ipsilateral theta power over the left frontal area. These findings advance the understanding of the \\u0026ldquo;spectrotopic\\u0026rdquo; nature of vibrotactile frequency processing in the cortex and may be relevant to future vibrotactile therapeutic strategies for pain.\\u003c/p\\u003e\"},{\"header\":\"Results\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eParticipant Demographics and Clinical Characteristics \\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eA total of 20 participants completed the study, comprising 9 females and 11 males. The mean age was 32.8 ± 7.2 years (age range: 23-45 years). As planned, the stimulation voltage was individually calibrated using a staircase method to induce a significant vibration sensation (rating of 7 on the NRS) in all participants.\\u0026nbsp;On average,\\u0026nbsp;participants reported pain catastrophizing scale score of 10.7 ± 4.2, depression score of 2.2 ± 1.6 and anxiety score of 4.2 ± 1.4, indicating the absence of clinically significant pain catastrophizing, anxiety or depression.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eEEG Effects\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eModulation of Resting Baseline Power by Vibrotactile Stimulation\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe EEG bandwidth activity was compared between vibrotactile stimulation conditions and resting baseline as measured over the electrode sites (\\u003cstrong\\u003eFigs. 1 and 3\\u003c/strong\\u003e, event-related spectral perturbations; \\u003cstrong\\u003eFigs. 2 and 4\\u003c/strong\\u003e, topographic patterns). \\u0026nbsp;\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e2 Hz Stimulation:\\u0026nbsp;\\u003c/strong\\u003etheta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 2.9) (\\u003cstrong\\u003eFigs. 1 and 2, left panels\\u003c/strong\\u003e). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4, P4 and C3 electrodes, all Ps \\u0026lt; 0.05, maximum effect at P4 electrode, t = 4.6). Delta, beta, low- and high- gamma frequency bands did not show significant changes.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e6 Hz Stimulation:\\u0026nbsp;\\u003c/strong\\u003etheta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 4.8) (\\u003cstrong\\u003eFigs. 1 and 2, middle panels\\u003c/strong\\u003e). Moreover, there was theta power enhancement over the frontal area with lateralization to the ipsilateral hemisphere (significant effects at the F3 and Fz electrodes, both Ps \\u0026lt; 0.05, maximum effect at F3 electrode, t = 4.9). Alpha frequency bands showed power decreases over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, all Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 3.0). Delta, beta, low- and high- gamma frequency bands did not show significant changes.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e12 Hz Stimulation:\\u0026nbsp;\\u003c/strong\\u003etheta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 3.0) (\\u003cstrong\\u003eFigs. 1 and 2, right panels\\u003c/strong\\u003e). A nonsignificant trend emerged for theta power increase at the F3 and Fz electrodes (both Ps \\u0026gt; 0.05). Alpha frequency bands showed power decreases over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, all Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 4.7). Delta, beta, low- and high- gamma frequency bands did not show significant changes.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e20 Hz Stimulation:\\u0026nbsp;\\u003c/strong\\u003etheta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 3.2) (\\u003cstrong\\u003eFigs. 3 and 4, left panels\\u003c/strong\\u003e). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4 and C3 electrodes, all Ps \\u0026lt; 0.05, maximum effect at C3 electrode, t = 3.3). Delta, beta, low- and high- gamma frequency bands did not show significant changes.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e40 Hz Stimulation:\\u0026nbsp;\\u003c/strong\\u003etheta power increased over the central area with lateralization to the contralateral hemisphere (significant effects at the C4 and P4 electrodes, both Ps \\u0026lt; 0.05, maximum effect at P4 electrode, t = 3.1) (\\u003cstrong\\u003eFigs. 3 and 4, right panels\\u003c/strong\\u003e). Alpha frequency bands showed power decreases over the central area bilaterally (significant effects at the C4, P4 and C3 electrodes, all Ps \\u0026lt; 0.05, maximum effect at C4 electrode, t = 3.4). Delta, beta, low- and high- gamma frequency bands did not show significant changes.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e----- Figures 1, 2, 3, 4 approximately here -----\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eComparison of Power Modulations Induced by Vibrotactile Stimulation\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFigures 5 and 6\\u003c/strong\\u003e show the mean power values across five patterns of vibrotactile stimulation (2 Hz, 6 Hz, 12 Hz, 20 Hz and 40 Hz stimulation) relative to resting baseline. The power was examined in an ANOVA with within-subject’s factors Stimulation (1) - (5) × Electrode (1) - (7). In case of significant interaction Stimulation × Electrode, indicating an overall difference between vibrotactile stimulation conditions with regard to the power as a function of the electrode, we ran separate ANOVAs for each electrode (see the “Statistical Analyses” section).\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eDelta band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 1.7, P = 0.14, did not prove significant, but interaction Stimulation × Electrode, F(6,456) = 2.4, P \\u0026lt; 0.001, was significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode (\\u003cstrong\\u003eFig. 5, left panels\\u003c/strong\\u003e). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 8.0, P \\u0026lt; 0.001, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in delta power at the Fz electrode in response to 40 Hz stimulation compared to 2 Hz (P \\u0026lt; 0.04), 6 Hz (P \\u0026lt; 0.03) and 12 Hz (P \\u0026lt; 0.02) stimulation. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 10.0, P \\u0026lt; 0.001, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a similar pattern of delta power decrease at the F3 electrode induced by 40 Hz stimulation as compared to stimulation at 6 Hz (P \\u0026lt; 0.005) and 12 Hz (P \\u0026lt; 0.002). At the F4 electrode, the main effect of the stimulation proved significant, F(4,76) = 3.2, P \\u0026lt; 0.02, indicating that delta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in delta power at the F4 electrode in response to 40 Hz stimulation compared to 6 Hz (P \\u0026lt; 0.02) stimulation. The C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 1.0, 2.3, 0.7 and 0.9, and P = 0.42, 0.07, 0.61 and 0.48, respectively, indicating that delta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 40 Hz stimulation inhibited delta power over the frontal areas.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eTheta band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 30.7, P \\u0026lt; 0.001, and interaction Stimulation × Electrode, F(6,456) = 7.6, P \\u0026lt; 0.001, were significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode (\\u003cstrong\\u003eFig. 5, middle panels\\u003c/strong\\u003e). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 13.4, P \\u0026lt; 0.001, indicating that theta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant increase in theta power at the Fz electrode in response to 6 Hz stimulation compared to 2 Hz (P \\u0026lt; 0.003), 12 Hz (P \\u0026lt; 0.004), 20 Hz (P \\u0026lt; 0.001) and 40 Hz (P \\u0026lt; 0.001) stimulation. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 30.2, P \\u0026lt; 0.001, indicating that theta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a similar pattern of theta power increase at the F3 electrode induced by 6 Hz stimulation as compared to stimulation at 2 Hz (P \\u0026lt; 0.001), 12 Hz (P \\u0026lt; 0.001), 20 Hz (P \\u0026lt; 0.001) and 40 Hz (P \\u0026lt; 0.001). The F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.0, 1.2, 2.1, 0.9 and 0.3, and P = 0.10, 0.31, 0.09, 0.48 and 0.9, respectively, indicating that theta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 6 Hz stimulation was effective in inducing frontal theta power enhancement over the central frontal and left frontal areas.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAlpha band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 21.4, P \\u0026lt; 0.001, and interaction Stimulation × Electrode, F(6,456) = 2.3, P \\u0026lt; 0.001, were significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode (\\u003cstrong\\u003eFig. 5, right panels\\u003c/strong\\u003e). We conducted separate ANOVAs for each electrode. At the Fz electrode, the main effect of the stimulation proved significant, F(4,76) = 2.5, P \\u0026lt; 0.05, indicating that alpha power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant decrease in alpha power at the Fz electrode in response to 40 Hz stimulation compared to 6 Hz stimulation (P \\u0026lt; 0.02). At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 5.7, P \\u0026lt; 0.001, indicating that alpha power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed alpha power decrease at the F3 electrode induced by 20 Hz stimulation as compared to stimulation at 6 Hz (P \\u0026lt; 0.003) and 12 Hz (P \\u0026lt; 0.02). The F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.2, 1.6, 1.7, 0.2 and 0.3, and P = 0.08, 0.19, 0.15, 0.92 and 0.88, respectively, indicating that alpha power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 20 Hz and 40 Hz stimulations inhibited frontal alpha power over the left frontal and central frontal areas, respectively.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eBeta band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 0.6, P = 0.72, did not prove significant, but interaction Stimulation × Electrode, F(6,456) = 2.2, P \\u0026lt; 0.002, was significant, indicating an overall difference between stimulation conditions with regard to mean power as a function of the electrode (\\u003cstrong\\u003eFig. 6, left panels\\u003c/strong\\u003e). We conducted separate ANOVAs for each electrode. At the F3 electrode, the main effect of the stimulation proved significant, F(4,76) = 3.7, P \\u0026lt; 0.009, indicating that beta power changed across conditions of vibrotactile stimulation. The Helmert contrasts revealed a significant increase in beta power at the F3 electrode in response to 6 Hz stimulation compared to 12 Hz stimulation (P \\u0026lt; 0.02). The Fz, F4, C3, C4, P3 and P4 electrodes: the main effect of the stimulation did not prove significant, F(4,76) = 2.2, 2.3, 0.6, 0.7, 2.0 and 2.1, and P = 0.08, 0.07, 0.67, 0.24, 0.10 and 0.09, respectively, indicating that beta power at these electrodes were not significantly modulated with the use of a vibrotactile stimulation. These findings imply that 6 Hz stimulation induced frontal beta power over the left frontal area.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eLow-gamma band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 1.4, P = 0.23, and interaction Stimulation × Electrode, F(6,456) = 0.9, P = 0.60, did not prove significant, indicating that low-gamma power was not significantly modulated with the use of a vibrotactile stimulation (\\u003cstrong\\u003eFig. 6, middle panels\\u003c/strong\\u003e).\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eHigh-gamma band.\\u003c/strong\\u003e The main effect of the stimulation, F(6,456) = 0.7, P = 0.61, and interaction Stimulation × Electrode, F(6,456) = 0.8, P = 0.63, did not prove significant, indicating that high-gamma power was not significantly modulated with the use of a vibrotactile stimulation (\\u003cstrong\\u003eFig. 6, right panels\\u003c/strong\\u003e). \\u0026nbsp;\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e----- Figures 5, 6 approximately here -----\\u003c/strong\\u003e\\u003c/p\\u003e\"},{\"header\":\"Discussion\",\"content\":\"\\u003cp\\u003eAlthough vibrotactile stimulation has demonstrated therapeutic potential, the cortical mechanisms underlying frequency-specific somatosensory processing remain poorly characterized. This study revealed that different vibration frequencies produce distinct patterns of cortical spectral modulation, suggesting a \\\"spectrotopic\\\" organization of vibrotactile processing. Of particular clinical relevance, 6 Hz stimulation uniquely enhanced theta power in the left frontal region - an electrophysiological signature previously associated with successful pain relief in both chronic pain patients and experimental settings. These findings advance our fundamental understanding of how the brain processes tactile frequency information and suggest potential mechanistic pathways by which vibrotactile stimulation may modulate pain perception.\\u003c/p\\u003e \\u003cp\\u003eAmong the tested frequencies, only 6 Hz stimulation significantly increased frontal theta power, while 2 Hz and 12 Hz showed minor, non-significant increases. Higher frequencies (20 Hz and 40 Hz) produced slight, non-significant decreases in frontal theta power. These distinct responses suggest frequency-specific theta rhythm dynamics in the frontal cortex during distinct frequencies of vibrotactile stimulation. The most pronounced effect was enhanced synchronization of theta oscillations over frontal areas involving F3 electrode during 6 Hz stimulation, corresponding to the left prefrontal cortex \\u003csup\\u003e\\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e22\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e23\\u003c/span\\u003e\\u003c/sup\\u003e. Neuromodulation studies suggest that increased activity in the prefrontal cortical areas plays a crucial role in pain management \\u003csup\\u003e\\u003cspan citationid=\\\"CR24\\\" class=\\\"CitationRef\\\"\\u003e24\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e25\\u003c/span\\u003e\\u003c/sup\\u003e. The prefrontal cortex is involved in cognitive and regulatory functions, and through its connections to different functional brain networks, plays a role in cognitive and emotional control over pain \\u003csup\\u003e\\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e26\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e27\\u003c/span\\u003e\\u003c/sup\\u003e.\\u003c/p\\u003e \\u003cp\\u003eFrom an electrophysiological standpoint, successful pain relief, both in chronic pain patients and in the context of experimental pain relief, was found to be associated with an increase in the left prefrontal theta activity \\u003csup\\u003e\\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e19\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e20\\u003c/span\\u003e\\u003c/sup\\u003e. A previous study demonstrated the effectiveness of frontal theta reinforcement in patients with chronic upper extremity pain using a vibrotactile BCI neurofeedback system, which resulted in reductions in both pain severity and pain interference scores \\u003csup\\u003e\\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e21\\u003c/span\\u003e\\u003c/sup\\u003e. During vibrotactile BCI therapy, the magnitude of frontal theta power increase at F3 electrode positively correlated with pain relief. This specificity to theta rhythms, absent in other frequency bands, underscores its unique role in pain reduction. Thus, an increase in frontal theta power may contribute to the analgesic effects of vibration stimulation, but further research is needed to elucidate the neural circuits underlying these effects.\\u003c/p\\u003e \\u003cp\\u003eOur study replicated several established patterns of cortical activity during tactile stimulation. Vibrotactile stimulation induced a significant decrease in alpha power over the central area compared to the resting state. The latter is referred to as alpha-event-related desynchronization (ERD), a well-known phenomenon during both non-nociceptive and nociceptive stimulation, likely related to nonspecific arousal and attention to stimuli \\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR3\\\" class=\\\"CitationRef\\\"\\u003e3\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e\\u003c/sup\\u003e. It can be inferred that vibrotactile stimulation enhances the excitability of sensorimotor cortical neurons, leading to a decrease in alpha power, which is consistent with previous studies \\u003csup\\u003e\\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e15\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e29\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e30\\u003c/span\\u003e\\u003c/sup\\u003e. Numerous imaging studies have shown that desynchronized alpha power emerges concurrently with increased activity in the sensorimotor cortex during motor tasks \\u003csup\\u003e\\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e31\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR32\\\" class=\\\"CitationRef\\\"\\u003e32\\u003c/span\\u003e\\u003c/sup\\u003e. Thus, alpha suppression is unlikely to be a phenomenon specific to pure somatosensation. Vibration stimulation also resulted in an increase in theta power over the central area compared to the resting state. Theta oscillations are recognized for their involvement in attentional processes \\u003csup\\u003e\\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e33\\u003c/span\\u003e\\u003c/sup\\u003e. Therefore, the increased theta power in the sensorimotor cortex likely reflects heightened attention to the sensory stimulation, as the brain processes both visual and tactile inputs. This event-related synchronization (ERS) of theta rhythms showed a lateralized pattern, with stronger activation in the somatosensory area opposite to the stimulated hand - a pattern consistent with the brain's contralateral processing of sensory information. These findings are consistent with known bilateral cortical representation of somatosensation with lateralization to the contralateral somatosensory cortex \\u003csup\\u003e\\u003cspan citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e34\\u003c/span\\u003e\\u003c/sup\\u003e. Notably, theta power modulation in the sensorimotor area may be associated with both tactile and painful stimulation \\u003csup\\u003e\\u003cspan citationid=\\\"CR2\\\" class=\\\"CitationRef\\\"\\u003e2\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e28\\u003c/span\\u003e,\\u003cspan additionalcitationids=\\\"CR36\\\" citationid=\\\"CR35\\\" class=\\\"CitationRef\\\"\\u003e35\\u003c/span\\u003e\\u0026ndash;\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003e37\\u003c/span\\u003e\\u003c/sup\\u003e. Thus, these findings are not likely to be specific to vibrotactile stimulation.\\u003c/p\\u003e \\u003cp\\u003eThis study has the following limitations. Our sample size was limited to 20 participants. While vibrotactile stimulation serves as a useful model for studying the underlying brain mechanisms of frequency processing and developing novel treatment approaches, our results should be tested in patients with chronic pain before drawing broader conclusions.\\u003c/p\\u003e \\u003cp\\u003eIn conclusion, our findings demonstrated that vibrotactile stimulation produces distinct frequency-dependent patterns of cortical activation, advancing our understanding of how the brain processes tactile frequency information. A key finding was that 6 Hz stimulation of the left index finger selectively enhanced theta power in the left prefrontal cortex - an electrophysiological signature previously linked to successful pain reduction in both clinical and experimental settings. These results provide a mechanistic foundation for developing novel vibration-based therapies in the future.\\u003c/p\\u003e\"},{\"header\":\"Materials and Methods\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eEthical Approval\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThis study was approved by the institutional review board of Washington University School of Medicine in St. Louis. All experimental procedures conformed to the standards set by the latest revision of the Declaration of Helsinki. All participants provided written informed consent before participation in the study. \\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eParticipants\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThis was a study with a single group consisting of 20 healthy participants. Healthy participants for the experiment were recruited through advertising the study via ads posting flyers at Washington University School of Medicine in St. Louis. Willing participants have been screened for inclusion and exclusion criteria. Inclusion criteria for the study were healthy male or female participants of any age between 18 and 50 years, with no major conditions of any organ system. Participants were excluded if they had any history of acute or chronic pain condition including episodic primary headaches, acute or chronic illness, or a diagnosed psychiatric disorder. To avoid any confounding by recent administration of pain medications, participants did not take any analgesics including non-steroidal anti-inflammatory drugs (NSAIDs) or acetaminophen for at least five drug half-lives prior to any study visit. Participants did not use caffeinated products for 3 h before the study as these can also affect electroencephalographic recording \\u003csup\\u003e38\\u003c/sup\\u003e. After screening and obtaining written informed consent, participants were asked to provide basic demographic information and to complete the Pain Catastrophizing Scale, Beck Depression Inventory and Beck Anxiety Inventory questionnaires \\u003csup\\u003e39-41\\u003c/sup\\u003e.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eExperimental Paradigm\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe study took place in a quiet study room with minimal outside disturbance. During the calibration phase, the vibrotactile stimulus intensity required to elicit a rating of 7 on a 0–10 Numerical Rating Scale (NRS) was determined, where 0 = no sensation, 3 = first instance of tactile sensation, 5 = moderate tactile sensation, 7 = significant tactile sensation, and 10 = first instance of pain. The stimulation voltage was individually calibrated using a staircase method, involving incremental increases and decreases in intensity (ranging from 10 to 30 V), applied to the left index fingertip until a rating of 7 on the NRS was reached three times. These parameters were subsequently used during the experimental phase. During this phase, participants were seated comfortably in a chair and instructed to minimize their movements during EEG data collection. Throughout the experiment, the participants were instructed to fixate on a fixation cross presented centrally on the screen to avoid excessive eye blinking while keeping their eyes open. Brain activity was recorded by means of EEG during two consecutive states: resting baseline and vibrotactile stimulation (\\u003cstrong\\u003eFig. 7\\u003c/strong\\u003e). Resting baseline: baseline EEG was recorded for 5 minutes during which participants were instructed not to perform any mental activity or have any specific thoughts but to remain calm and relaxed as much as possible, while not falling asleep. Vibrotactile stimulation: vibrotactile stimuli were delivered to the tip of the left index finger using five different types of stimuli corresponding to delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz) frequencies, with 20 trials conducted for each frequency. Because neural activities can be modulated by attention during the stimulus presentation \\u003csup\\u003e42,43\\u003c/sup\\u003e, the participants were asked to pay attention to all stimuli. The stimulation voltage was individually calibrated to induce significant tactile sensation (refer to the calibration phase described earlier in this paragraph). The stimulus duration of each trial was 5 sec, with an inter-stimulus interval of 5, 6, or 7 sec, and all trials and inter-stimulus intervals were randomized.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003e----- Figure 7 approximately here -----\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eElectroencephalogram Recording and Processing \\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eElectroencephalogram (EEG) was recorded by means of 24 wireless dry electrodes mounted on the EEG headset in an International 10–20 System (DSI 24, Wearable Sensing, San Diego, CA, USA). EEG was referenced to the Pz electrode, sampled at 600 Hz with a ground electrode placed on the forehead. Electrode impedance was kept below 10 kΩ. The raw EEG data were preprocessed in MATLAB environment (Mathworks, Nattick, MA, USA). Continuous EEG recording was band-pass filtered between 1 and 100 Hz using a finite impulse response (FIR) filter. To remove environmental noise, 60 Hz notch filter was applied. EEG data were screened for extreme values, as well as for infrequent and unstereotyped artifacts. For further artifact attenuation, Infomax independent component analysis (ICA) was applied \\u003csup\\u003e44,45\\u003c/sup\\u003e. Independent components found to reflect eye blinks, lateral eye movements, muscle-related and cardiac artifacts were removed from the data. EEG data were common average re-referenced. Frequency bands were defined as follows: delta, 1–3 Hz; theta, 4–7 Hz; alpha, 8–13 Hz; beta, 14– 29 Hz; low-gamma, 30–58 Hz; high-gamma, 62–100 Hz \\u003csup\\u003e1,46\\u003c/sup\\u003e. \\u0026nbsp; \\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eTime-frequency analysis\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eTime-frequency analysis was performed in MATLAB environment (Mathworks, Nattick, MA, USA) \\u003csup\\u003e3\\u003c/sup\\u003e. The EEG data were segmented into stimulus-locked epochs from −1,000 to 7,000 msec, with time 0 corresponding to the onset of vibrotactile stimulation. A Morlet wavelet convolution was computed. Two hundred time points were generated, and 100 linearly spaced frequencies were computed from 1 to 100 Hz. Variable cycles were used for low and high frequencies, with 3 cycles for lowest frequencies and up to 15 cycles for highest frequencies. This variable cycle allows the wavelet convolution method to provide a better frequency resolution at lower frequencies and a better temporal resolution at higher frequencies. Event-related spectral perturbations (ERSP) \\u003csup\\u003e47,48\\u003c/sup\\u003e were computed in decibels relative to the resting baseline. Specific frequency bands were defined as follows: delta (1-3 Hz) theta (4-7 Hz), alpha (8-12 Hz), beta (13-29 Hz), low-gamma (30-59 Hz) and high-gamma (62-100 Hz) \\u003csup\\u003e1,3\\u003c/sup\\u003e. The ERSP value for each time-frequency point was calculated for each participant. Topographic patterns of brain activity were illustrated for a value representing the mean activity at each frequency band. For each participant, the time-frequency data were averaged across all trials per condition. The grand average time-frequency maps were obtained by averaging data across all participants for each condition.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eStatistical Analyses\\u0026nbsp;\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eWe used non-parametric statistical inference to compare the EEG bandwidth activity between vibrotactile stimulation conditions and resting baseline that does not make assumptions on the distributions of the data \\u003csup\\u003e49-51\\u003c/sup\\u003e. Permutation tests were performed across participants for random effects inference. All statistical tests were two-tailed with a significance level of 0.05. Under the null hypothesis of no difference in the EEG data between the vibrotactile stimulation and resting baseline, the electrode labels for each participant were randomly permuted between conditions and the resulting data were used to compute a permutation t-statistic spatiotemporal electrode map for the power. Repeating this permutation procedure 1,000 times, using Monte Carlo random sampling, enabled us to estimate the empirical distribution of the t-statistic at each electrode, and thus convert the original data into a p-value statistical map. Lastly, to control for multiple comparisons across all electrodes, the p-values were adjusted using a false discovery rate (FDR) procedure. The significant values with P ≤ 0.05 were retained while values with P \\u0026gt; 0.05 were set to zero.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003eDifferences in the mean power values between vibrotactile stimulation conditions were examined in a repeated-measures ANOVA with within-subject’s factors Stimulation (main factor with five levels: 2 Hz, 6 Hz, 12 Hz, 20 Hz and 40 Hz vibrotactile stimulation - see the “Experimental Paradigm” section) × Electrode (F3, Fz, F4, C3, C4, P3 and P4). In case of significant interaction Stimulation × Electrode, indicating an overall difference between conditions with regard to the power as a function of the electrode, we ran separate ANOVAs for each electrode. Planned contrasts were then used to test a priori hypotheses and decompose the significant effects of vibrotactile stimulation. All statistical tests were two tailed with a significance level of 0.05, and the P-values were adjusted using an FDR correction.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eAcknowledgments\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe authors thank study participants for their time and effort. This study did not receive any funding. \\u0026nbsp;\\u0026nbsp; \\u0026nbsp;\\u003c/p\\u003e\\n\\n\\u003cp\\u003e\\u003cstrong\\u003eAuthor Contributions\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eN.R. performed the experiment and data collection, performed the data analysis, and wrote the manuscript. P.D. aided in software development, and data collection. Z.H. aided in hardware development. S.M. wrote the manuscript. S.H. wrote the manuscript. E.C.L. oversaw engineering and electrophysiology-related implementation, supervised the project, and wrote the manuscript. All authors reviewed the manuscript. \\u0026nbsp;\\u0026nbsp;\\u003c/p\\u003e\\n\\n\\u003cp\\u003e\\u003cstrong\\u003eData Availability\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eThe data will be made available upon reasonable request to the corresponding author.\\u003c/p\\u003e\\n\\n\\u003cp\\u003e\\u003cstrong\\u003eDisclosures\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eECL has stock ownership in Neurolutions, Inner Cosmos, Aurenar, and Sora Neuroscience. Washington University also owns stock in Neurolutions. This work and E.C. Leuthardt have had their conflict of interest rigorously evaluated and managed throughout this study and with creation of this manuscript. SH has received consultancy fees from Vertex and research funding from Eli Lilly, unrelated to the presented work. The remaining authors have no conflicts of interest to declare.\\u003c/p\\u003e\\n\\n\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003ePloner, M., Sorg, C. \\u0026amp; Gross, J. Brain Rhythms of Pain. \\u003cem\\u003eTrends in cognitive sciences\\u003c/em\\u003e \\u003cstrong\\u003e21\\u003c/strong\\u003e, 100-110, doi:10.1016/j.tics.2016.12.001 (2017).\\u003c/li\\u003e\\n\\u003cli\\u003eNorthon, S., Rustamov, N. \\u0026amp; Pich\\u0026eacute;, M. Cortical integration of bilateral nociceptive signals: when more is less. \\u003cem\\u003ePain\\u003c/em\\u003e \\u003cstrong\\u003e160\\u003c/strong\\u003e, 724-733, doi:10.1097/j.pain.0000000000001451 (2019).\\u003c/li\\u003e\\n\\u003cli\\u003eRustamov, N., Northon, S., Tessier, J., Leblond, H. \\u0026amp; Pich\\u0026eacute;, M. 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A comparison of random field theory and permutation methods for the statistical analysis of MEG data. \\u003cem\\u003eNeuroImage\\u003c/em\\u003e \\u003cstrong\\u003e25\\u003c/strong\\u003e, 383-394, doi:10.1016/j.neuroimage.2004.09.040 (2005).\\u003c/li\\u003e\\n\\u003cli\\u003eMaris, E. \\u0026amp; Oostenveld, R. Nonparametric statistical testing of EEG- and MEG-data. \\u003cem\\u003eJournal of neuroscience methods\\u003c/em\\u003e \\u003cstrong\\u003e164\\u003c/strong\\u003e, 177-190, doi:10.1016/j.jneumeth.2007.03.024 (2007).\\u003c/li\\u003e\\n\\u003cli\\u003eRustamov, N., Humphries, J., Carter, A. \\u0026amp; Leuthardt, E. C. Theta-gamma coupling as a cortical biomarker of brain-computer interface-mediated motor recovery in chronic stroke. \\u003cem\\u003eBrain communications\\u003c/em\\u003e \\u003cstrong\\u003e4\\u003c/strong\\u003e, fcac136, doi:10.1093/braincomms/fcac136 (2022).\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":true,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"scientific-reports\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"scirep\",\"sideBox\":\"Learn more about [Scientific Reports](http://www.nature.com/srep/)\",\"snPcode\":\"\",\"submissionUrl\":\"\",\"title\":\"Scientific Reports\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Scientific Reports\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":true},\"keywords\":\"Vibrotactile Stimulation, Power Spectra, Frontal Theta Power\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-6043161/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-6043161/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eWhile scientific research has extensively explored how the brain integrates touch and pain signals, the cerebral processing of specific vibrotactile frequencies remains poorly understood. This gap is particularly significant given clinical evidence that vibrotactile stimulation can reduce pain in both chronic pain patients and experimental settings. Our study investigated the cortical electrophysiological correlates of peripheral vibrotactile stimulation across different frequencies in healthy volunteers, with a focus on frequency-dependent patterns of neuronal activation. While electroencephalogram (EEG) was recorded, healthy participants received vibrotactile stimulation to the left index fingertip at frequencies corresponding to established neural rhythms: delta (2 Hz), theta (6 Hz), alpha (12 Hz), beta (20 Hz), and gamma (40 Hz). We compared the EEG bandwidth activity between vibrotactile stimulation conditions relative to resting baseline. Our findings demonstrated that vibrotactile stimulation produces distinct frequency-dependent patterns of cortical activation. A key finding was that 6 Hz stimulation selectively enhanced theta power in the left prefrontal cortex - an electrophysiological signature previously linked to successful pain relief. These findings advance the understanding of the \\\"spectrotopic\\\" nature of vibrotactile frequency processing in the cortex and provide a mechanistic foundation for developing novel vibration-based therapies in the future.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Cortical Spectral Dynamics of Vibrotactile Frequency Processing\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2025-02-21 17:03:03\",\"doi\":\"10.21203/rs.3.rs-6043161/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"decision\",\"content\":\"Revision requested\",\"date\":\"2025-05-14T03:27:46+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2025-05-12T08:55:57+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"256421588706082832223502789916771913491\",\"date\":\"2025-04-21T06:32:03+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"editorInvitedReview\",\"content\":\"\",\"date\":\"2025-04-04T01:57:31+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewerAgreed\",\"content\":\"270835736268004735653280349443302088012\",\"date\":\"2025-03-25T00:48:30+00:00\",\"index\":\"hide\",\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2025-03-20T06:25:32+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2025-03-19T01:04:41+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvited\",\"content\":\"\",\"date\":\"2025-02-20T21:50:05+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"checksComplete\",\"content\":\"\",\"date\":\"2025-02-19T09:56:28+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Scientific Reports\",\"date\":\"2025-02-16T21:48:29+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"scientific-reports\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"scirep\",\"sideBox\":\"Learn more about [Scientific Reports](http://www.nature.com/srep/)\",\"snPcode\":\"\",\"submissionUrl\":\"\",\"title\":\"Scientific Reports\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"stoa\",\"reportingPortfolio\":\"Scientific Reports\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"cba3b163-b20f-47cd-adae-76c0a246b6a2\",\"owner\":[],\"postedDate\":\"February 21st, 2025\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"under-review\",\"subjectAreas\":[{\"id\":44651253,\"name\":\"Biological sciences/Neuroscience\"},{\"id\":44651254,\"name\":\"Biological sciences/Physiology\"}],\"tags\":[],\"updatedAt\":\"2025-08-04T08:39:15+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2025-02-21 17:03:03\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-6043161\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-6043161\",\"identity\":\"rs-6043161\",\"version\":[\"v1\"]},\"buildId\":\"8U1c8b4HqxoKbykW_rLl7\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}