Repetitive Transcranial Magnetic Stimulation over Right PMd Does Not Affect the Stability of Rhythmic Bimanual Finger Movements.

How the brain controls rhythmic asymmetric bimanual movements remains an enduring question in neuroscience. Prior research suggests that the right dorsal premotor cortex (PMd) is essential for maintaining asymmetric bimanual rhythmic finger-tapping patterns. However, such findings have not fully accounted for evidence showing that asymmetric movements impose greater cognitive control demands than symmetric ones. Thus, previously observed disruptions following transient disruption of right PMd may reflect impaired cognitive control rather than motor processes specific to asymmetry. To test this, we manipulated cognitive control demands during bimanual tapping by having participants synchronize movements with regularly flickering visual stimuli. Switching from spatially congruent to symbolic cues reduces tapping stability similarly to switching from symmetric to asymmetric patterns, providing a platform to test the cognitive control hypothesis. Right PMd was targeted with 1 Hz repetitive transcranial magnetic stimulation (rTMS) intended to transiently reduce excitability. Participants (15 females, 13 males) completed symmetric and asymmetric tapping tasks across multiple frequencies. Performance was compared with a sham session. Contrary to expectations, rTMS-related alterations in tapping stability and accuracy were not dependent on movement symmetry or cognitive control demands. Instead, no detectable behavioral effect of rTMS was observed under the present stimulation and testing conditions. These results indicate that asymmetric rhythmic tapping can be maintained after rTMS over right PMd, although lacking direct measures of PMd target engagement limits conclusions regarding cortical perturbation effectiveness. Future work incorporating concurrent neural measures can determine the mechanisms underlying this null effect.