Dual-site beta transcranial alternating current stimulation during a bimanual coordination task modulates functional connectivity between motor areas

Abstract

Background

Communication within brain networks depends on functional connectivity. One promising approach to modulate such connectivity between cortical areas is dual-site transcranial alternating current stimulation (tACS), which non-invasively applies weak alternating currents to two brain areas.

Objectives

In the current study, we aimed to modulate inter-regional functional connectivity with dual-site tACS to bilateral primary motor cortices (M1s) during bimanual coordination and, in turn, alter behaviour.

Methods

Using functional magnetic resonance imaging (fMRI), we recorded participants’ brain responses during a bimanual coordination task in a concurrent tACS-fMRI design. While performing a slow and fast version of the task, participants received one of three types of beta (20 Hz) dual-site tACS over both M1s: zero-phase, jittered-phase or sham, in a within-participant, repeated measures design.

Results

While we did not observe any significant tACS effects on behaviour, the study revealed an attenuation effect of zero-phase tACS on interhemispheric connectivity. Additionally, the two active types of tACS (zero-phase and jittered-phase) differed in the task-related M1 connectivity with other motor cortical regions, such as premotor cortex and supplementary motor area. Furthermore, individual E-field strengths were related to functional connectivity in the zero-phase condition.

Conclusions

Dual-site beta tACS over both M1s altered functional connectivity between motor areas. However, this effect did not translate significantly to the behavioural level in the presence of a restricted sample size. Future studies may thus integrate mechanistic measures, such as measures of interhemispheric inhibition, to strengthen causal interpretations.