Cortical dynamics underlying motor skill acquisition: Insights from sequential and random practice using transcranial...

Motor skill training induces neuroplastic changes in the primary motor cortex, leading to improvements in motor performance, as demonstrated by transcranial magnetic stimulation (TMS) studies. However, the specific intracortical mechanisms driving these changes are not fully understood. Our study therefore employed combined TMS-electroencephalography (TMS-EEG) to investigate the cortical dynamics associated with motor skill acquisition, comparing sequential and random practice. Eighteen healthy adults participated in the study. Participants performed a serial reaction time task, pressing buttons quickly with the four fingers. Participants attended three sessions: performing the task in a predetermined sequence (learning condition, LC), in a random sequence (non-learning condition, NC), or resting without engaging in the task (control condition, CC). Motor-evoked potentials (MEPs) and TMS-evoked potentials (TEPs) were measured before and after motor training. Consequently, reaction time significantly improved over time in LC (all P < 0.001), with no improvement observed in NC (all P > 0.3). MEP amplitude significantly decreased after NC (P = 0.021), while no changes were found in LC or CC (all P > 0.41). TEPs showed a specific modulation of the N45 component following LC (P < 0.05). However, no significant correlation was observed between changes in the N45 component and reaction time in LC (all P > 0.2). The N45 component is specifically modulated by sequential learning, potentially reflecting cortical processes of motor skill acquisition. However, the absence of a correlation with reaction time suggests that this component is not a sufficiently sensitive index of changes in motor performance.