Beta Frequency Dual-Site tACS Applied Over the Primary Motor Cortices Increased Interhemispheric Inhibition

Shannae Daley

Emerging research indicates that when applied concurrently to two distant cortical regions, transcranial alternating current stimulation (tACS) can potentially enhance communication between the stimulated brain regions. Impaired functional connectivity is often associated with various psychiatric and neurodevelopmental disorders, making tACS a promising intervention tool that merits further exploration of its mechanisms for enhancing functional connectivity. The current study compared the effects of dual-site beta tACS (ds-tACS) to a sham control stimulation in 38 healthy adults (26 females; 18-37 yrs) to experimentally investigate the effect of tACS on interhemispheric inhibition (IHI), the neural mechanism by which one cerebral hemisphere attenuates the activity of the contralateral hemisphere, facilitating the coordination of motor and cognitive functions. ds-tACS was applied at beta frequency (20Hz) over the bilateral primary motor cortices (M1), where research has shown anatomical and functional interactions applying phase-synchronised stimulation for 20 min at rest, with the aim of increasing functional connectivity. IHI was assessed using transcranial magnetic stimulation (TMS), and manual dexterity performance was assessed using a purdue pegboard test (PPT). Results demonstrated a significant improvement in IHI following ds-tACS, a pattern not observed during the sham session. Additionally, ds-tACS selectively improved bimanual dexterity, while no such improvement was noted in the unimanual conditions. This study advanced the mechanistic understanding of how tACS modulates functional connectivity and the potential of tACS to significantly impact the field of neurorehabilitation and mental health treatment, offering hope for improved outcomes in diverse clinical populations.

Beta Frequency Dual-Site tACS Applied Over the Primary Motor Cortices Increased Interhemispheric Inhibition

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