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Functional Connectivity Changes in the Primary Motor Cortex Induced by Dual-Site Transcranial Alternating Current Stimulation : A Source-Level Analysis
Hagen, Joris Johannes (2025) Functional Connectivity Changes in the Primary Motor Cortex Induced by Dual-Site Transcranial Alternating Current Stimulation : A Source-Level Analysis.
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| Abstract: | Background: Functional connectivity (FC) plays an essential role in motor control and is often disrupted in neurological disorders. Dual-site transcranial Alternating Current Stimulation (ds-tACS) is a method used to modulate FC between different brain regions, such as the left and right Primary Motor Cortices (M1s). A key parameter of ds-tACS is the phase-lag of the stimulation waveform between the stimulation sites, determining if the applied stimulation synchronizes or desynchronizes the underlying regions. This study tested the hypothesis that ds-tACS modulates interhemispheric FC in a phase-specific manner. This study investigated how four different phase-lags affect the FC between left and right M1 in source space. A secondary aim was to investigate how different averaging methods of wPLI values of source pairs influence the detection of ds-tACS induced FC changes. Methods: Resting-state EEG data was analysed from a preliminary dataset of 25 participants, of which 20 participants were included, after receiving ds-tACS at 20Hz with four phase-lag conditions: InPhase, PiHalf, AntiPhase, 3HalfPi, and a sham condition. Source reconstruction was performed using the eLORETA algorithm. FC was quantified using the weighted Phase Lag Index (wPLI) for the beta-band (13-30Hz). To assess phase-specific FC modulation, both global averaging and Hierarchical Clustering (HCC) were applied on post-stimulation wPLI values, with and without anatomical constraints based on whether sources were spatially adjacent to each other. HCC clustering with anatomical constraints was also applied to the pre-stimulus recording to ensure fixed clustering between participants, conditions and segments. Statistical significance was assessed using the Wilcoxon signed-rank and the Hermans-Rasson test. Results: Using global averaging, no significant modulation of FC was found after Bonferroni correction. However, when using anatomically constrained HCC, the PiHalf condition increased FC compared to Sham and other active conditions across multiple cluster combinations. In contrast, the InPhase condition showed a decrease in FC. This behaviour also showed when analyzing the data with fixed clustering. The adjusted Rand Index (ARI) found low clustering consistency for HCC without anatomical constraints (0.02), but increased when anatomical constraints were applied (0.2). Fixed clustering showed ARI values of 0.15 for the left hemisphere and 0.07 for the right hemisphere. Conclusions: This preliminary study demonstrated that ds-tACS at 20Hz, applied to the M1s, modulated FC, with PiHalf increasing and InPhase decreasing FC. The limited sensitivity of global averaging approaches suggests the importance of spatially informed clustering techniques. Anatomically constrained HCC improved clustering consistency, but further methodological improvements are needed. |
| Item Type: | Essay (Master) |
| Faculty: | EEMCS: Electrical Engineering, Mathematics and Computer Science |
| Subject: | 30 exact sciences in general |
| Programme: | Biomedical Engineering MSc (66226) |
| Link to this item: | https://purl.utwente.nl/essays/106578 |
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