Connectivity changes following transcranial alternating current stimulation at 5-Hz: an EEG study

Connectivity changes following transcranial alternating current stimulation at 5-Hz: an EEG study | 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 Short Report Connectivity changes following transcranial alternating current stimulation at 5-Hz: an EEG study Tien-Wen Lee, Gerald Tramontano This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4582437/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Introduction Transcranial alternating current stimulation (tACS) at 5-Hz to the right hemisphere can alleviate anxiety symptoms. This study aimed to explore the connectivity changes following the treatment. Methods We collected electroencephalography (EEG) data from 24 participants with anxiety disorders before and after the tACS treatment during a single session. Electric stimulation was applied over the right hemisphere, with 1.0 mA at F4, 1.0 mA at P4, and 2.0 mA at T8, following the 10–10 EEG convention. With eLORETA, the scalp signals were transformed into the cortex’s current source density. We assessed the connectivity changes at theta frequency between the centers of Brodmann area (BA) 6/8 (frontal), BA 39/40 (parietal), and BA 21 (middle temporal). Functional connectivity was indicated by lagged coherences and lagged phase synchronization. Paired t-tests were used to quantify the differences statistically. Results We observed enhanced lagged phase synchronization at theta frequency between the frontal and parietal regions ( P = 0.002) and between the parietal and temporal regions ( P = 0.005), after Bonferroni correction. Conclusion Applying tACS 5-Hz over the right hemisphere enhanced inter-regional interaction, which was spectrum-specific and mainly mediated by phase, rather than power, synchrony. The potential neural mechanisms are discussed. Computational Neuroscience Transcranial alternating current stimulation (tACS) Transcranial electrical stimulation (tES) Electroencephalography (EEG) Exact low-resolution electromagnetic tomography (eLORETA) Coherence Phase Synchronization Connectivity Figures Figure 1 Introduction Transcranial alternating current stimulation (tACS) can influence cortical rhythm and activity (Antal et al., 2008 ; Bland and Sale, 2019 ). Recently, tACS has been proposed as an anxiolytic option (Clancy et al., 2018 ). Lee et al. reported that 5-Hz tACS at 2.0 mA over the right hemisphere with the currents oscillating between T8 and F4/P4 (10–10 EEG convention) could alleviate anxiety symptoms effectively (Lee et al., 2024 ), called tripod design. It was found that the therapeutic effects were associated with an increase in alpha power and a decrease in beta and gamma power (Lee and Tramontano, 2024 ), concordant with previous literature about neural markers of anxiety reduction (Engel et al., 2009 ; Spitzer and Haegens, 2017 ; Oathes et al., 2008 ; Miskovic et al., 2010 ; Berger, 1929 ; Sharma and Singh, 2015 ). Despite the consistency in the clinical and electrophysiological profiles, enhanced theta power was predicted based on the popular entrainment theory but was not observed (Helfrich et al., 2014 ; Voss et al., 2014 ). Instead, as stated above, the influence of tACS affected broad spectra (spectrum-unspecific), and accounting for the holistic picture of the neural consequences of tACS required the collaboration of several imperative network mechanisms (Lee and Tramontano, 2024 ). Although FDA-approved tACS, Neurotone-101, was introduced in 1970s, the influence of tACS on brain connectivity is much less addressed (Shekelle et al., 2018 ; Clancy et al., 2018 ). To supplement previous findings that focused on regional powers, the primary purpose of this study was to investigate the functional connectivity changes to 5-Hz tripod tACS between the frontal, parietal, and temporal regions. The effect of tACS was built upon its influences on neuronal activities, i.e., changes in firing rate and spike timing (Anastassiou et al., 2010 ; Radman et al., 2007 ; Radman et al., 2009 ). A recent invasive primate study suggested that tACS may influence the timing, not the rate, of spiking activity within the targeted brain region (Krause et al., 2019 ). Such an effect is frequency- and location-specific. Administering in-phase alternating currents at two separate brain regions is thus expected to synchronize their activities and enhance their connection through neural plasticity (Levy and Steward, 1983 ; Markram et al., 2012 ). We postulated that the connectivity strength between the frontal, parietal, and temporal areas would increase after tACS, and the increment was spectrum specific, opposite to power changes. To fulfill the brain-based approach, exact low-resolution brain electromagnetic tomography (eLORETA) was exploited to transform EEG data from the scalp to the gray matter voxels of a template brain (Pascual-Marqui, 2007a ; Jurcak et al., 2007 ). The relationships between the current source density (CSD) time series of different brain regions at distinct spectra were evaluated by lagged coherence and phase synchronization, with the former a linear and the latter a nonlinear index of functional connectivity (Pascual-Marqui, 2007b ). Materials and Methods Participants We reviewed the data collected from our clinics between 2018 and 2022 after obtaining approval from a private Review Board (Pearl IRB; https://www.pearlirb.com/ ). Twenty-four anxiety patients who received 5-Hz tACS treatment over the right hemisphere and had pre- and post-treatment EEGs were identified. As for detailed clinical profiles and the methodology of tACS, please refer to our other relevant reports (Lee et al., 2024 ; Lee and Tramontano, 2024 ). tACS, EEG recording, and pre-processing The tACS montage of electrodes covered the right lateral side of the head at F4, T8, and P4 positions in terms of the 10–10 EEG convention. The peak current intensity for T4 was 2.0 mA, while those at F4 and P4 were 1.0 mA. Alternating sinewave currents oscillated at 5 Hz between electrodes T4 and F4/P4 for 25 minutes. Before and after the tACS treatment, we used the Brainmaster device ( https://brainmaster.com/ ) to acquire 10 min eye-open digital EEG data at 256 samples/sec with linked-ear reference. The EEG traces were edited using the Software EEGLAB (Delorme and Makeig, 2004 ). A band-pass filter (1–50 Hz) was applied to preprocess the data, followed by automatic artifact removal. A single rater (TW Lee) manually eliminated any remaining noisy portions. The clean EEG data, which included the removal of various artifacts such as blinks and eye movements, were then segmented into 2-second epochs and imported into eLORETA for further analyses. eLORETA analyses The eLORETA is a tomographic method for deriving electric neuronal activity from EEG by computing a weighted minimum norm inverse solution, where the weights are adaptive to the data (data-dependent) (Pascual-Marqui, 2007a ; Jurcak et al., 2007 ). Any arbitrary point-test sources can be correctly computed with exact, zero-error localization. eLORETA utilizes the principles of linearity and superposition to effectively identify distributed electric sources (i.e., CSD) within the brain cortex (a template with 6,239 gray matter voxels), although its spatial resolution may be limited. The CSD time series were decomposed to those of the following power spectrum, delta (1–4 Hz), theta (4–8 Hz; the focus of this study), alpha (8–12 Hz), low beta (12–15 Hz), mid-to-high beta (15–30 Hz), and low gamma (30–45 Hz). Connectivity and statistical analyses Lagged (general) coherence and phase synchronization were adopted to represent linear and nonlinear functional connectivity strengths, respectively (Pascual-Marqui, 2007b ). Both were derived from the CSD time series of the selected voxel. The equations to obtain the latter are the same as the former except for a pre-normalization step to discount the influence of power, hence non-linear. Namely, the relationship between amplitudes did not affect phase synchronization. Total coherence is the sum of the lagged and instantaneous dependence, and the latter contains confounds from the “non-physiological contribution due to volume conduction and low spatial resolution” (Pascual-Marqui, 2007b ). Accordingly, the instantaneous part was disregarded in this report (the same reason for the lagged phase synchronization). The average connectivity strengths were calculated between three coordinates, which were the center of Brodmann area (BA) 6/8 (frontal; [25,0,50]), BA 39/40 (parietal; [45,-50,35]), and BA 21 (middle temporal; [60,-15,-15]). Paired t-tests were used to examine the connectivity changes before and after the tACS (3 connections in total). Results The mean age of the 24 selected patients was 34.6 (SD 14.2), ranging from 15.2 to 54. The gender ratio male to female was 9:15. Our hypothesis was verified that the connectivity strengths were increased after the 5-Hz tACS tripod treatment. The enhancement was statistically significant for phase synchronization after multiple comparison corrections. It was noted in the connections between the frontal and parietal regions and between the parietal and temporal areas, not between the frontal and temporal counterparts. The connectivity strengths and the statistics are summarized in Table 1, and the results with P < 0.05 are illustrated in Figure 1. Supplementary analyses disclosed that the connectivity changes were only present in the theta range, not in other spectra (spectrum-specific; data not shown). Discussion This research studied the connectivity strength changes after tACS at 5-Hz and 2.0 mA for 25 minutes, with a tripod montage covering the frontal, parietal, and temporal regions. The design was proposed as a way to ease anxiety (Lee et al., 2024 ). Pre- and post-treatment EEGs were collected and analyzed for 24 participants using an imaging method eLORETA, which converted the signals recorded at the scalp to CSD in the brain cortex. Average functional connectivity was thus derived from the CSD time series between the frontal, parietal, and temporal regions. After tACS treatment, the lagged phase synchronization at theta range (i.e., spectrum-specific) significantly increased in the frontal–parietal and the parietal–temporal connections. The lagged coherence was enhanced between the frontal and parietal regions with a P value lower than 0.05, although not surviving Bonferroni correction. Our hypothesis was generally verified but with some caveats, discussed below. Strong evidence suggested that tACS may influence the timing of neuronal spikes (Krause et al., 2019 ; Anastassiou et al., 2010 ; Radman et al., 2007 ). When tACS is delivered to two distinct brain regions, the firing of neural tissues in these regions is expected to synchronize more closely by the applied frequency. Furthermore, given that the recorded EEGs were not in real-time with the delivered tACS, the significant inter-regional interactions indicated the engagement of a plasticity mechanism. Interestingly, the index derived from lagged phase synchronization was more robust than that of lagged coherence. Our previous study investigating the regional power changes to tACS demonstrated complicated spectral power features incompatible with entrainment theory (Lee and Tramontano, 2024 ). From a mathematical perspective, the formula of phase synchronization is similar to that of coherence, except for a normalization procedure to discount the influence of the power. Based on the two analytic results (power and connectivity), it was deduced that the inter-regional modulatory effects of tACS were not due to the concurrent entrained oscillation/power at multiple regions. Rather, it was through synchronizing their phase relationship, echoing previous neurophysiological research that recorded and investigated spike timing under tACS (Krause et al., 2019 ). Compatible with our conjecture, Vossen et al. explored the aftereffects of alpha tACS and concluded that the modulatory effect of tACS was mediated by plasticity rather than entrainment (Vossen et al., 2015 ). In summary, at the large-scale network level, the inter-regional influence of tACS was mediated by synchronization in phase (crosstalk), not by the concurrent entrainment of powers (regional profile). It was noticed that the connectivity changes were not significant between the frontal and temporal regions. Again, if the influence of tACS on neural connectivity mainly worked through concurrent entrainment across targeted areas, the interactions between the three explored regions would tighten altogether. We inferred that the differential manifestations originated from the discrepancy in the hardwire underpinnings. It was noted that the superior longitudinal fasciculus (SLF) bridges between the frontal and parietal regions and between the inferior parietal cortex (BA39/40) and the middle temporal cortex (BA 21) (SLF III). The former constitutes the frontoparietal network, and the latter links the two cortical nodes of the default-mode network (Lee and Xue, 2018 ). No white matter “highway” exists between the dorsolateral prefrontal and middle temporal cortices (note: the inferior frontal cortex and anterior temporal region are connected by uncinate fasciculus). It hints at one of the most paramount plasticity mechanisms, spike-time-dependent plasticity, which requires direct axonal connections to take effect (Levy and Steward, 1983 ; Markram et al., 2012 ). It was observed that applying a particular frequency of tACS can “entrain” or “synchronize” the neural oscillations to match the frequency of the electrical stimulation (Helfrich et al., 2014 ; Voss et al., 2014 ), framed as an entrainment theory. However, our recent report demonstrated that narrow band 5-Hz tACS desynchronized neural oscillation (offline measurement and comparison), which affected broad spectra beyond the default frequency of tACS (Lee and Tramontano, 2024 ). An earlier study by Brignani et al. challenged the idea that tACS effectively modulated brain oscillations (Brignani et al., 2013 ). Alexander et al. showed that 10-Hz tACS, in fact, reduced alpha power in the frontal region (Alexander et al., 2019 ). In addition, Lafton et al. applied the intracranial recording and observed no sleep rhythm entrainment to tACS (Lafon et al., 2017 ). The contradictory findings cannot be resolved by entrainment theory alone but require a broader mechanism to reconcile them. Agreeing with Vossen et al. (Vossen et al., 2015 ), we regard that neural plasticity could be a better candidate to accommodate the offline (in contrast to real-time) tACS influence on regional powers and inter-regional interactions. Nevertheless, we cannot exclude the possibility that injecting an artificial narrow-band alternating current may interfere with underlying neural synchronization under certain conditions, given our previous analysis and several other reports summarized above (Lee and Tramontano, 2024 ). It is noteworthy that even if tACS impedes the underlying neural synchronization, it may still be beneficial. In our previous report, power reduction in the right hemisphere due to tACS might reduce emotion reactivity according to emotion lateralization theory and hence, might catalyze the anxiolytic effect (Lee and Tramontano, 2024 ; Ross, 2021 ). The merits and demerits of tACS thus could be context-dependent, which requires further research to clarify. Conclusion The neural influence of tACS is still under active investigation. This research explored the connectivity changes following 5-Hz tACS over the right hemisphere. Increased lagged phase synchronization at theta spectrum was noticed between frontal and parietal regions and between parietal and temporal regions. The enhancement in functional connectivity was likely mediated by its influence on neural spike timing and spike-time-dependent plasticity. Declarations Authors Contributions Both authors contributed intellectually to this work. TW Lee carried out the analysis and wrote the first draft. Both authors revised and approved the final version of the manuscript. Acknowledgments This work was supported by NeuroCognitive Institute (NCI) and NCI Clinical Research Foundation Inc. We would like to thank Almeida Sergio for helping prepare the research material. Financial support N/A. Both authors declare no conflicts of interest. 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Induction of self awareness in dreams through frontal low current stimulation of gamma activity. Nat Neurosci , 17(6), 810-2. doi:10.1038/nn.3719. Vossen, A., Gross, J., & Thut, G. (2015). Alpha Power Increase After Transcranial Alternating Current Stimulation at Alpha Frequency (alpha-tACS) Reflects Plastic Changes Rather Than Entrainment. Brain Stimul , 8(3), 499-508. doi:10.1016/j.brs.2014.12.004. Table Table 1 is available in the Supplementary Files section Additional Declarations The authors declare no competing interests. Supplementary Files Table1.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-4582437","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Short Report","associatedPublications":[],"authors":[{"id":314525728,"identity":"fd618c43-af06-4eec-b834-01b53927834c","order_by":0,"name":"Tien-Wen Lee","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Tien-Wen","middleName":"","lastName":"Lee","suffix":""},{"id":314525729,"identity":"bddfd87f-e7fa-4bab-87c2-ffdd67ba2344","order_by":1,"name":"Gerald Tramontano","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA4ElEQVRIiWNgGAWjYJADxgdQugG/OjYIJQHEzAYka2GTIMox8vG9Dz/dqLhTxz+7+Vh1QcXhfH72ww0MPyq24dRieIzdWDrnzDMJiTvH0m7POHPYcmZPYgNjz5nbuLW0sTFI57YdlmC4kWN2m7ftsIHBDcYGZsY2vFqYf4O0yAO1FPP+I0KLPBsbG9gWA6AWZt4GIrQYsKWxWeecOSy58UZasjTPsXQDSaBfDuLzi3zzMebbORWH+eVuJB/8zFNjbcDPfvzhgx8VeGw5gE0UqyDclgZ8sqNgFIyCUTAKQAAADaVTsSf6/ZkAAAAASUVORK5CYII=","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Gerald","middleName":"","lastName":"Tramontano","suffix":""}],"badges":[],"createdAt":"2024-06-14 13:40:41","currentVersionCode":1,"declarations":{"humanSubjects":true,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":true,"humanSubjectConsent":true,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-4582437/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4582437/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":58590107,"identity":"fd713605-447e-440b-9d96-325272f2020c","added_by":"auto","created_at":"2024-06-18 15:08:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":105922,"visible":true,"origin":"","legend":"\u003cp\u003eLeft: The lagged coherence was increased in the frontoparietal network. Right: The lagged phase synchronization was increased in both the frontoparietal network and parietal-temporal connection.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4582437/v1/8dad7fa733f2b41c9cf32cbb.png"},{"id":58590677,"identity":"a6b6ec45-19e5-4b42-9375-ef18865c6a36","added_by":"auto","created_at":"2024-06-18 15:16:31","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":420052,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4582437/v1/993b368c-9569-49e1-8c73-f37216589f77.pdf"},{"id":58590676,"identity":"1e8a948f-2f12-4270-8104-a08edc2002b6","added_by":"auto","created_at":"2024-06-18 15:16:27","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":14622,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.docx","url":"https://assets-eu.researchsquare.com/files/rs-4582437/v1/f383ed2f7ba19b9122d548d1.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eConnectivity changes following transcranial alternating current stimulation at 5-Hz: an EEG study\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTranscranial alternating current stimulation (tACS) can influence cortical rhythm and activity (Antal et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Bland and Sale, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Recently, tACS has been proposed as an anxiolytic option (Clancy et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Lee et al. reported that 5-Hz tACS at 2.0 mA over the right hemisphere with the currents oscillating between T8 and F4/P4 (10\u0026ndash;10 EEG convention) could alleviate anxiety symptoms effectively (Lee et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), called tripod design. It was found that the therapeutic effects were associated with an increase in alpha power and a decrease in beta and gamma power (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), concordant with previous literature about neural markers of anxiety reduction (Engel et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Spitzer and Haegens, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Oathes et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Miskovic et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Berger, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1929\u003c/span\u003e; Sharma and Singh, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDespite the consistency in the clinical and electrophysiological profiles, enhanced theta power was predicted based on the popular entrainment theory but was not observed (Helfrich et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Voss et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Instead, as stated above, the influence of tACS affected broad spectra (spectrum-unspecific), and accounting for the holistic picture of the neural consequences of tACS required the collaboration of several imperative network mechanisms (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Although FDA-approved tACS, Neurotone-101, was introduced in 1970s, the influence of tACS on brain connectivity is much less addressed (Shekelle et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Clancy et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). To supplement previous findings that focused on regional powers, the primary purpose of this study was to investigate the functional connectivity changes to 5-Hz tripod tACS between the frontal, parietal, and temporal regions.\u003c/p\u003e \u003cp\u003eThe effect of tACS was built upon its influences on neuronal activities, i.e., changes in firing rate and spike timing (Anastassiou et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Radman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Radman et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). A recent invasive primate study suggested that tACS may influence the timing, not the rate, of spiking activity within the targeted brain region (Krause et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Such an effect is frequency- and location-specific. Administering in-phase alternating currents at two separate brain regions is thus expected to synchronize their activities and enhance their connection through neural plasticity (Levy and Steward, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Markram et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). We postulated that the connectivity strength between the frontal, parietal, and temporal areas would increase after tACS, and the increment was spectrum specific, opposite to power changes.\u003c/p\u003e \u003cp\u003eTo fulfill the brain-based approach, exact low-resolution brain electromagnetic tomography (eLORETA) was exploited to transform EEG data from the scalp to the gray matter voxels of a template brain (Pascual-Marqui, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007a\u003c/span\u003e; Jurcak et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The relationships between the current source density (CSD) time series of different brain regions at distinct spectra were evaluated by lagged coherence and phase synchronization, with the former a linear and the latter a nonlinear index of functional connectivity (Pascual-Marqui, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2007b\u003c/span\u003e).\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eParticipants\u003c/h2\u003e \u003cp\u003eWe reviewed the data collected from our clinics between 2018 and 2022 after obtaining approval from a private Review Board (Pearl IRB; \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.pearlirb.com/\u003c/span\u003e\u003cspan address=\"https://www.pearlirb.com/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). Twenty-four anxiety patients who received 5-Hz tACS treatment over the right hemisphere and had pre- and post-treatment EEGs were identified. As for detailed clinical profiles and the methodology of tACS, please refer to our other relevant reports (Lee et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003etACS, EEG recording, and pre-processing\u003c/h2\u003e \u003cp\u003eThe tACS montage of electrodes covered the right lateral side of the head at F4, T8, and P4 positions in terms of the 10\u0026ndash;10 EEG convention. The peak current intensity for T4 was 2.0 mA, while those at F4 and P4 were 1.0 mA. Alternating sinewave currents oscillated at 5 Hz between electrodes T4 and F4/P4 for 25 minutes. Before and after the tACS treatment, we used the Brainmaster device (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://brainmaster.com/\u003c/span\u003e\u003cspan address=\"https://brainmaster.com/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e) to acquire 10 min eye-open digital EEG data at 256 samples/sec with linked-ear reference.\u003c/p\u003e \u003cp\u003eThe EEG traces were edited using the Software EEGLAB (Delorme and Makeig, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). A band-pass filter (1\u0026ndash;50 Hz) was applied to preprocess the data, followed by automatic artifact removal. A single rater (TW Lee) manually eliminated any remaining noisy portions. The clean EEG data, which included the removal of various artifacts such as blinks and eye movements, were then segmented into 2-second epochs and imported into eLORETA for further analyses.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eeLORETA analyses\u003c/h2\u003e \u003cp\u003eThe eLORETA is a tomographic method for deriving electric neuronal activity from EEG by computing a weighted minimum norm inverse solution, where the weights are adaptive to the data (data-dependent) (Pascual-Marqui, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2007a\u003c/span\u003e; Jurcak et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Any arbitrary point-test sources can be correctly computed with exact, zero-error localization. eLORETA utilizes the principles of linearity and superposition to effectively identify distributed electric sources (i.e., CSD) within the brain cortex (a template with 6,239 gray matter voxels), although its spatial resolution may be limited. The CSD time series were decomposed to those of the following power spectrum, delta (1\u0026ndash;4 Hz), theta (4\u0026ndash;8 Hz; the focus of this study), alpha (8\u0026ndash;12 Hz), low beta (12\u0026ndash;15 Hz), mid-to-high beta (15\u0026ndash;30 Hz), and low gamma (30\u0026ndash;45 Hz).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eConnectivity and statistical analyses\u003c/h2\u003e \u003cp\u003eLagged (general) coherence and phase synchronization were adopted to represent linear and nonlinear functional connectivity strengths, respectively (Pascual-Marqui, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2007b\u003c/span\u003e). Both were derived from the CSD time series of the selected voxel. The equations to obtain the latter are the same as the former except for a pre-normalization step to discount the influence of power, hence non-linear. Namely, the relationship between amplitudes did not affect phase synchronization. Total coherence is the sum of the lagged and instantaneous dependence, and the latter contains confounds from the \u0026ldquo;non-physiological contribution due to volume conduction and low spatial resolution\u0026rdquo; (Pascual-Marqui, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2007b\u003c/span\u003e). Accordingly, the instantaneous part was disregarded in this report (the same reason for the lagged phase synchronization).\u003c/p\u003e \u003cp\u003eThe average connectivity strengths were calculated between three coordinates, which were the center of Brodmann area (BA) 6/8 (frontal; [25,0,50]), BA 39/40 (parietal; [45,-50,35]), and BA 21 (middle temporal; [60,-15,-15]). Paired t-tests were used to examine the connectivity changes before and after the tACS (3 connections in total).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eThe mean age of the 24 selected patients was 34.6 (SD 14.2), ranging from 15.2 to 54. The gender ratio male to female was 9:15. Our hypothesis was verified that the connectivity strengths were increased after the 5-Hz tACS tripod treatment. The enhancement was statistically significant for phase synchronization after multiple comparison corrections. It was noted in the connections between the frontal and parietal regions and between the parietal and temporal areas, not between the frontal and temporal counterparts. The connectivity strengths and the statistics are summarized in Table 1, and the results with \u003cem\u003eP\u003c/em\u003e \u0026lt; 0.05 are illustrated in Figure 1. Supplementary analyses disclosed that the connectivity changes were only present in the theta range, not in other spectra (spectrum-specific; data not shown).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThis research studied the connectivity strength changes after tACS at 5-Hz and 2.0 mA for 25 minutes, with a tripod montage covering the frontal, parietal, and temporal regions. The design was proposed as a way to ease anxiety (Lee et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Pre- and post-treatment EEGs were collected and analyzed for 24 participants using an imaging method eLORETA, which converted the signals recorded at the scalp to CSD in the brain cortex. Average functional connectivity was thus derived from the CSD time series between the frontal, parietal, and temporal regions. After tACS treatment, the lagged phase synchronization at theta range (i.e., spectrum-specific) significantly increased in the frontal\u0026ndash;parietal and the parietal\u0026ndash;temporal connections. The lagged coherence was enhanced between the frontal and parietal regions with a \u003cem\u003eP\u003c/em\u003e value lower than 0.05, although not surviving Bonferroni correction. Our hypothesis was generally verified but with some caveats, discussed below.\u003c/p\u003e \u003cp\u003eStrong evidence suggested that tACS may influence the timing of neuronal spikes (Krause et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Anastassiou et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Radman et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). When tACS is delivered to two distinct brain regions, the firing of neural tissues in these regions is expected to synchronize more closely by the applied frequency. Furthermore, given that the recorded EEGs were not in real-time with the delivered tACS, the significant inter-regional interactions indicated the engagement of a plasticity mechanism. Interestingly, the index derived from lagged phase synchronization was more robust than that of lagged coherence. Our previous study investigating the regional power changes to tACS demonstrated complicated spectral power features incompatible with entrainment theory (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). From a mathematical perspective, the formula of phase synchronization is similar to that of coherence, except for a normalization procedure to discount the influence of the power. Based on the two analytic results (power and connectivity), it was deduced that the inter-regional modulatory effects of tACS were not due to the concurrent entrained oscillation/power at multiple regions. Rather, it was through synchronizing their phase relationship, echoing previous neurophysiological research that recorded and investigated spike timing under tACS (Krause et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Compatible with our conjecture, Vossen et al. explored the aftereffects of alpha tACS and concluded that the modulatory effect of tACS was mediated by plasticity rather than entrainment (Vossen et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In summary, at the large-scale network level, the inter-regional influence of tACS was mediated by synchronization in phase (crosstalk), not by the concurrent entrainment of powers (regional profile).\u003c/p\u003e \u003cp\u003eIt was noticed that the connectivity changes were not significant between the frontal and temporal regions. Again, if the influence of tACS on neural connectivity mainly worked through concurrent entrainment across targeted areas, the interactions between the three explored regions would tighten altogether. We inferred that the differential manifestations originated from the discrepancy in the hardwire underpinnings. It was noted that the superior longitudinal fasciculus (SLF) bridges between the frontal and parietal regions and between the inferior parietal cortex (BA39/40) and the middle temporal cortex (BA 21) (SLF III). The former constitutes the frontoparietal network, and the latter links the two cortical nodes of the default-mode network (Lee and Xue, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). No white matter \u0026ldquo;highway\u0026rdquo; exists between the dorsolateral prefrontal and middle temporal cortices (note: the inferior frontal cortex and anterior temporal region are connected by uncinate fasciculus). It hints at one of the most paramount plasticity mechanisms, spike-time-dependent plasticity, which requires direct axonal connections to take effect (Levy and Steward, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e1983\u003c/span\u003e; Markram et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt was observed that applying a particular frequency of tACS can \u0026ldquo;entrain\u0026rdquo; or \u0026ldquo;synchronize\u0026rdquo; the neural oscillations to match the frequency of the electrical stimulation (Helfrich et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Voss et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), framed as an entrainment theory. However, our recent report demonstrated that narrow band 5-Hz tACS desynchronized neural oscillation (offline measurement and comparison), which affected broad spectra beyond the default frequency of tACS (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). An earlier study by Brignani et al. challenged the idea that tACS effectively modulated brain oscillations (Brignani et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Alexander et al. showed that 10-Hz tACS, in fact, reduced alpha power in the frontal region (Alexander et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In addition, Lafton et al. applied the intracranial recording and observed no sleep rhythm entrainment to tACS (Lafon et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The contradictory findings cannot be resolved by entrainment theory alone but require a broader mechanism to reconcile them. Agreeing with Vossen et al. (Vossen et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), we regard that neural plasticity could be a better candidate to accommodate the offline (in contrast to real-time) tACS influence on regional powers and inter-regional interactions. Nevertheless, we cannot exclude the possibility that injecting an artificial narrow-band alternating current may interfere with underlying neural synchronization under certain conditions, given our previous analysis and several other reports summarized above (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). It is noteworthy that even if tACS impedes the underlying neural synchronization, it may still be beneficial. In our previous report, power reduction in the right hemisphere due to tACS might reduce emotion reactivity according to emotion lateralization theory and hence, might catalyze the anxiolytic effect (Lee and Tramontano, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Ross, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The merits and demerits of tACS thus could be context-dependent, which requires further research to clarify.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe neural influence of tACS is still under active investigation. This research explored the connectivity changes following 5-Hz tACS over the right hemisphere. Increased lagged phase synchronization at theta spectrum was noticed between frontal and parietal regions and between parietal and temporal regions. The enhancement in functional connectivity was likely mediated by its influence on neural spike timing and spike-time-dependent plasticity.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthors Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBoth\u0026nbsp;authors\u0026nbsp;contributed intellectually to this work. TW Lee\u0026nbsp;carried out the analysis\u0026nbsp;and\u0026nbsp;wrote the first draft.\u0026nbsp;Both\u0026nbsp;authors revised and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by\u0026nbsp;NeuroCognitive Institute (NCI) and\u0026nbsp;NCI Clinical Research Foundation Inc. We would like to thank Almeida Sergio for helping prepare the research material.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFinancial support\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eN/A.\u003c/p\u003e\n\u003cp\u003eBoth authors declare no conflicts of interest.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with ethical standards\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research analyzed the databank collected from 2018 to 2022. The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAlexander, M. L., Alagapan, S., Lugo, C. E., Mellin, J. M., Lustenberger, C., Rubinow, D. R., et al. (2019). Double-blind, randomized pilot clinical trial targeting alpha oscillations with transcranial alternating current stimulation (tACS) for the treatment of major depressive disorder (MDD). \u003cem\u003eTransl Psychiatry\u003c/em\u003e, 9(1), 106. doi:10.1038/s41398-019-0439-0.\u003c/li\u003e\n \u003cli\u003eAnastassiou, C. A., Montgomery, S. M., Barahona, M., Buzsaki, G., \u0026amp; Koch, C. (2010). The effect of spatially inhomogeneous extracellular electric fields on neurons. \u003cem\u003eJ Neurosci\u003c/em\u003e, 30(5), 1925-36. doi:10.1523/JNEUROSCI.3635-09.2010.\u003c/li\u003e\n \u003cli\u003eAntal, A., Boros, K., Poreisz, C., Chaieb, L., Terney, D., \u0026amp; Paulus, W. (2008). Comparatively weak after-effects of transcranial alternating current stimulation (tACS) on cortical excitability in humans. \u003cem\u003eBrain Stimul\u003c/em\u003e, 1(2), 97-105. doi:10.1016/j.brs.2007.10.001.\u003c/li\u003e\n \u003cli\u003eBerger, H. (1929). Ueber das elektroenkephalogramm des menschen. \u003cem\u003eArchiv f\u0026uuml;r Psychiatrie und Nervenkrankheiten\u003c/em\u003e, 87(1), 527-570.\u003c/li\u003e\n \u003cli\u003eBland, N. S., \u0026amp; Sale, M. V. (2019).\u0026nbsp;Current challenges: the ups and downs of tACS. \u003cem\u003eExp Brain Res\u003c/em\u003e, 237(12), 3071-3088. doi:10.1007/s00221-019-05666-0.\u003c/li\u003e\n \u003cli\u003eBrignani, D., Ruzzoli, M., Mauri, P., \u0026amp; Miniussi, C. (2013). Is transcranial alternating current stimulation effective in modulating brain oscillations? \u003cem\u003ePLoS One\u003c/em\u003e, 8(2), e56589. doi:10.1371/journal.pone.0056589.\u003c/li\u003e\n \u003cli\u003eClancy, K. J., Baisley, S. K., Albizu, A., Kartvelishvili, N., Ding, M., \u0026amp; Li, W. (2018). 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(2014).\u0026nbsp;Entrainment of brain oscillations by transcranial alternating current stimulation. \u003cem\u003eCurr Biol\u003c/em\u003e, 24(3), 333-9. doi:10.1016/j.cub.2013.12.041.\u003c/li\u003e\n \u003cli\u003eJurcak, V., Tsuzuki, D., \u0026amp; Dan, I. (2007).\u0026nbsp;10/20, 10/10, and 10/5 systems revisited: their validity as relative head-surface-based positioning systems. \u003cem\u003eNeuroimage\u003c/em\u003e, 34(4), 1600-11. doi:10.1016/j.neuroimage.2006.09.024.\u003c/li\u003e\n \u003cli\u003eKrause, M. R., Vieira, P. G., Csorba, B. A., Pilly, P. K., \u0026amp; Pack, C. C. (2019). Transcranial alternating current stimulation entrains single-neuron activity in the primate brain. \u003cem\u003eProc Natl Acad Sci U S A\u003c/em\u003e, 116(12), 5747-5755. doi:10.1073/pnas.1815958116.\u003c/li\u003e\n \u003cli\u003eLafon, B., Henin, S., Huang, Y., Friedman, D., Melloni, L., Thesen, T., et al. (2017). Low frequency transcranial electrical stimulation does not entrain sleep rhythms measured by human intracranial recordings. \u003cem\u003eNat Commun\u003c/em\u003e, 8(1), 1199. doi:10.1038/s41467-017-01045-x.\u003c/li\u003e\n \u003cli\u003eLee, T. W., Li, C. S., \u0026amp; Tramontano, G. (2024). Tripod transcranial alternating current stimulation at 5-Hz over right hemisphere may relieve anxiety symptoms: a preliminary report. \u003cem\u003eJournal of Affective Disorders\u003c/em\u003e, 360, 156-62.\u003c/li\u003e\n \u003cli\u003eLee, T. W., \u0026amp; Tramontano, G. (2024). Neural consequences of 5-Hz transcranial alternating current stimulation over right hemisphere: an eLORETA EEG study. \u003cem\u003eNeuroscience Letters\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eLee, T. W., \u0026amp; Xue, S. W. (2018). Functional connectivity maps based on hippocampal and thalamic dynamics may account for the default-mode network. \u003cem\u003eEur J Neurosci\u003c/em\u003e, 47(5), 388-398. doi:10.1111/ejn.13828.\u003c/li\u003e\n \u003cli\u003eLevy, W., \u0026amp; Steward, O. (1983). Temporal contiguity requirements for long-term associative potentiation/depression in the hippocampus. \u003cem\u003eNeuroscience\u003c/em\u003e, 8(4), 791-797.\u003c/li\u003e\n \u003cli\u003eMarkram, H., Gerstner, W., \u0026amp; Sj\u0026ouml;str\u0026ouml;m, P. J. (2012). Spike-timing-dependent plasticity: a comprehensive overview. \u003cem\u003eFrontiers in synaptic neuroscience\u003c/em\u003e, 4, 2.\u003c/li\u003e\n \u003cli\u003eMiskovic, V., Ashbaugh, A. R., Santesso, D. L., McCabe, R. E., Antony, M. M., \u0026amp; Schmidt, L. A. (2010). Frontal brain oscillations and social anxiety: a cross-frequency spectral analysis during baseline and speech anticipation. \u003cem\u003eBiol Psychol\u003c/em\u003e, 83(2), 125-32. doi:10.1016/j.biopsycho.2009.11.010\u003c/li\u003e\n \u003cli\u003eS0301-0511(09)00237-3 [pii].\u003c/li\u003e\n \u003cli\u003eOathes, D. J., Ray, W. J., Yamasaki, A. S., Borkovec, T. D., Castonguay, L. G., Newman, M. G., et al. (2008). Worry, generalized anxiety disorder, and emotion: Evidence from the eeg gamma band. \u003cem\u003eBiol Psychol\u003c/em\u003e, 79(2), 165-70. doi:10.1016/j.biopsycho.2008.04.005.\u003c/li\u003e\n \u003cli\u003ePascual-Marqui, R. D. (2007a). Discrete, 3D distributed, linear imaging methods of electric neuronal activity. Part 1: exact, zero error localization. \u003cem\u003earXiv preprint arXiv:0710.3341\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003ePascual-Marqui, R. D. (2007b). Instantaneous and lagged measurements of linear and nonlinear dependence between groups of multivariate time series: frequency decomposition. \u003cem\u003earXiv preprint arXiv:0711.1455\u003c/em\u003e.\u003c/li\u003e\n \u003cli\u003eRadman, T., Ramos, R. L., Brumberg, J. C., \u0026amp; Bikson, M. (2009). Role of cortical cell type and morphology in subthreshold and suprathreshold uniform electric field stimulation in vitro. \u003cem\u003eBrain Stimul\u003c/em\u003e, 2(4), 215-28, 228 e1-3. doi:10.1016/j.brs.2009.03.007.\u003c/li\u003e\n \u003cli\u003eRadman, T., Su, Y., An, J. H., Parra, L. C., \u0026amp; Bikson, M. (2007). Spike timing amplifies the effect of electric fields on neurons: implications for endogenous field effects. \u003cem\u003eJ Neurosci\u003c/em\u003e, 27(11), 3030-6. doi:10.1523/JNEUROSCI.0095-07.2007.\u003c/li\u003e\n \u003cli\u003eRoss, E. D. (2021). Differential hemispheric lateralization of emotions and related display behaviors: emotion-type hypothesis. \u003cem\u003eBrain Sciences\u003c/em\u003e, 11(8), 1034.\u003c/li\u003e\n \u003cli\u003eSharma, A., \u0026amp; Singh, M. (2015) \u0026apos;Assessing alpha activity in attention and relaxed state: An EEG analysis\u0026apos; \u003cem\u003e2015 1st International Conference on Next Generation Computing Technologies (NGCT)\u003c/em\u003e. IEEE, pp. 508-513.\u003c/li\u003e\n \u003cli\u003eShekelle, P. G., Cook, I. A., Miake-Lye, I. M., Mak, S., Booth, M. S., Shanman, R., et al. (2018). The effectiveness and risks of cranial electrical stimulation for the treatment of pain, depression, anxiety, PTSD, and insomnia: A systematic review.\u003c/li\u003e\n \u003cli\u003eSpitzer, B., \u0026amp; Haegens, S. (2017). Beyond the status quo: a role for beta oscillations in endogenous content (re) activation. \u003cem\u003eeneuro\u003c/em\u003e, 4(4).\u003c/li\u003e\n \u003cli\u003eVoss, U., Holzmann, R., Hobson, A., Paulus, W., Koppehele-Gossel, J., Klimke, A., et al. (2014). Induction of self awareness in dreams through frontal low current stimulation of gamma activity. \u003cem\u003eNat Neurosci\u003c/em\u003e, 17(6), 810-2. doi:10.1038/nn.3719.\u003c/li\u003e\n \u003cli\u003eVossen, A., Gross, J., \u0026amp; Thut, G. (2015). Alpha Power Increase After Transcranial Alternating Current Stimulation at Alpha Frequency (alpha-tACS) Reflects Plastic Changes Rather Than Entrainment. \u003cem\u003eBrain Stimul\u003c/em\u003e, 8(3), 499-508. doi:10.1016/j.brs.2014.12.004.\u003cstrong\u003e\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"NCI Clinical Research Foundation","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Transcranial alternating current stimulation (tACS), Transcranial electrical stimulation (tES), Electroencephalography (EEG), Exact low-resolution electromagnetic tomography (eLORETA), Coherence, Phase Synchronization, Connectivity","lastPublishedDoi":"10.21203/rs.3.rs-4582437/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4582437/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003eIntroduction\u003c/b\u003e\u003c/p\u003e \u003cp\u003eTranscranial alternating current stimulation (tACS) at 5-Hz to the right hemisphere can alleviate anxiety symptoms. This study aimed to explore the connectivity changes following the treatment.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eWe collected electroencephalography (EEG) data from 24 participants with anxiety disorders before and after the tACS treatment during a single session. Electric stimulation was applied over the right hemisphere, with 1.0 mA at F4, 1.0 mA at P4, and 2.0 mA at T8, following the 10\u0026ndash;10 EEG convention. With eLORETA, the scalp signals were transformed into the cortex\u0026rsquo;s current source density. We assessed the connectivity changes at theta frequency between the centers of Brodmann area (BA) 6/8 (frontal), BA 39/40 (parietal), and BA 21 (middle temporal). Functional connectivity was indicated by lagged coherences and lagged phase synchronization. Paired t-tests were used to quantify the differences statistically.\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eWe observed enhanced lagged phase synchronization at theta frequency between the frontal and parietal regions (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002) and between the parietal and temporal regions (\u003cem\u003eP\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.005), after Bonferroni correction.\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusion\u003c/b\u003e\u003c/p\u003e \u003cp\u003eApplying tACS 5-Hz over the right hemisphere enhanced inter-regional interaction, which was spectrum-specific and mainly mediated by phase, rather than power, synchrony. The potential neural mechanisms are discussed.\u003c/p\u003e","manuscriptTitle":"Connectivity changes following transcranial alternating current stimulation at 5-Hz: an EEG study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-18 15:08:22","doi":"10.21203/rs.3.rs-4582437/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9fa0d528-852e-44ed-96af-230891d41eef","owner":[],"postedDate":"June 18th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":33267069,"name":"Computational Neuroscience"}],"tags":[],"updatedAt":"2024-06-18T15:08:22+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-18 15:08:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4582437","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4582437","identity":"rs-4582437","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}