cTBS Over the Left Supplementary Motor Area (lSMA) Does Not Modulate Rhythmic Bimanual Coordination in the Presence and Absence of Visual Cues

Bimanual coordination modes, namely in-phase and anti-phase, represent two distinct movement patterns characterized by simultaneous & symmetrical movements of both hands and alternating complementary actions, respectively. These coordination modes are integral in various activities, such as playing musical instruments, typing, and participating in sports that demand precise hand-eye coordination. The objective of the present experiment was to investigate the impact of continuous theta burst stimulation (cTBS) targeting the left supplementary motor area (lSMA) on bimanual coordination during in/anti-phase coordination modes. To explore this, we utilized a steady-state system of coordination dynamics and evaluated the continuous relative phase ({phi}) and variability of relative phase (SD{phi}) during cued and non-cued trials in both pre- and post-transcranial magnetic stimulation (TMS) conditions. The results revealed that visual cues (cued trials) significantly enhanced bimanual coordination performance in both in/anti-phase coordination modes. However, contrary to expectations, the downregulation of lSMA through cTBS did not lead to significant disruptions in movement during in/anti-phase bimanual coordination in pre- and post-TMS stimulation. Potential factors for the lack of observed effects include methodological limitations, individual differences, and functional redundancy within the motor system. Further research is needed to optimize stimulation parameters, increase sample sizes, and explore the interactions between the lSMA, and other brain regions involved in motor control to gain a comprehensive understanding of the contributions of the lSMA in bimanual coordination.