Elucidating how Transcranial Alternating Current Stimulation Influences Functional Connectivity and Motor Performance via Electroencephalography

Lauren E Mobers

Previous research has established that concurrent transcranial alternating current stimulation (tACS) can enhance functional connectivity between distant cortical regions through the entrainment of neuronal oscillations, thus leading to improved cognitive and motor performance in both healthy and clinical populations. Yet, the mechanistic understanding of how tACS mediates such processes is limited. The current study aimed to address this gap by elucidating the underlying neurophysiological mechanisms in which tACS alters neuronal communication between targeted regions and how this influences motor performance. Healthy, right-handed young adults (N = 38, 27 females) underwent two separate experimental sessions: one involving 20Hz dual-site tACS and the other sham stimulation, both applied over the bilateral primary motor cortices (M1s). Resting-state electroencephalography was measured prior to, and following stimulation to assess functional connectivity between M1s, as quantified by the imaginary part of coherence. Bimanual motor performance was captured using the Purdue Pegboard task before and after stimulation. Contrasting the hypothesis, functional connectivity between M1s did not improve following tACS. However, bimanual motor performance improved, and spectral power analysis revealed a significant decrease in beta power following active tACS. These results indicate that functional connectivity via entrainment may not be responsible for behavioural improvements following tACS and that other mechanisms may be of importance. The observed decrease in beta-power following tACS represents a novel finding and suggests that the suppression of beta-power may be essential for enhancing motor performance. Ultimately, this study supports the use of dual-site tACS in healthy populations to improve motor functioning and has implications in applying tACS in clinical populations with motor dysfunction.

Elucidating how Transcranial Alternating Current Stimulation Influences Functional Connectivity and Motor Performance via Electroencephalography

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