Disentangling motor and cognitive roles of cortical beta oscillations and their modulation with rTMS

Cortical beta oscillations are central to motor control. These rhythms are modulated during movement preparation and execution, and are also sensitive to cognitive factors such as uncertainty, attention and reward prediction. However, the distinct motor and cognitive roles of cortical beta oscillations --roles that may inform condition-specific therapeutic strategies--remain unclear. This study aimed to disentangle the respective contributions of motor and cognitive functions, and to assess their modulation with repetitive transcranial magnetic stimulation (rTMS). Twenty-four healthy participants performed a visually cued reaching task in which directional uncertainty was dynamically manipulated by varying the number of targets in real-time. Reaction time was quantified as a behavioural measure. Three stimulation conditions were applied during the preparatory periods between the uncertainty and go cues: no stimulation, regular rTMS at each participants individual beta frequency, and irregular rTMS. Electroencephalography was used to measure beta-band oscillatory activity. Our results showed that uncertainty cues induced bilateral beta suppression, with greater uncertainty linked to smaller reductions in beta power. Movement-related beta modulation was lateralised to the hemisphere contralateral to the executing hand, where elevated beta power in the pre- go cue period predicted longer reaction times. Both regular and irregular rTMS significantly shortened reaction times and attenuated beta event-related desynchronisation. Reductions in beta desynchronisation correlated with improvements in reaction times, suggesting beta desynchronisation reflects a neural threshold for movement initiation. These findings indicate that cortical beta oscillations encode distinct motor and cognitive processes, and that beta frequency rTMS can modulate beta dynamics to facilitate faster movement initiation by lowering this neural threshold.