Transcranial magnetic stimulation investigations of reaching and grasping movements

Transcranial magnetic stimulation (TMS) has emerged as a suitable technique to investigate the network of cortical areas involved in human grasp/reach movements. Applied over the primary motor cortex (M1), TMS reveals the pattern of activation of different muscles during complex reaching-to-grasp tasks. Repetitive TMS (rTMS) used to induce “virtual lesions” of other cortical areas has allowed investigation of other cortical structures such as the ventral premotor cortex (PMv), dorsal premotor cortex (PMd) and the anterior intraparietal sulcus (aIPS). Each of these appears to contribute to specific aspects of reaching, grasping and lifting objects. Finally, twin-coil TMS studies can illustrate the time course of operation of parallel intracortical circuits that mediate functional connectivity between the PMd, PMv, the posterior parietal cortex and the primary motor cortices