Dynamic evolution of intracortical and corticomuscular connectivity during reach-and-grasp movement planning and execution

Reach and grasp movements involve a complex transformation of information from visual to motor space. Initially, task-related information is encoded in extrinsic, object-centered spatial coordinates, whereas motor output is represented in intrinsic, body-centered coordinates. In this study, effective connectivity was assessed using Partial Directed Coherence (PDC) to examine both intracortical and corticomuscular interactions during self-initiated reach and grasp actions. EEG signals from 16 cortical channels and EMG signals from 6 upper limb muscles were analyzed in 20 healthy right-handed participants (aged 18 to 45) performing vertical and lateral grasping tasks with a self-selected limb. Intracortical connectivity was evaluated across four distinct time windows spanning the planning and execution phases, while corticomuscular connectivity, defined as directed interactions from EEG to EMG, was assessed continuously from one second before to one second after movement onset. The results revealed that intracortical connectivity evolved dynamically across the premovement and execution phases, reflecting a continuous modulation of cortical interactions during motor planning and performance. Corticomuscular connectivity from EEG to EMG consistently decreased around movement onset across all evaluated conditions. Although some differences were observed between the PDC curves related to the grasp types and the used limb, they did not reach statistical significance after correction for multiple comparisons. These findings highlight the temporal specificity and task dependence of motor-related connectivity, offering insights into the distributed neural processes underlying sensorimotor transformations.