Human neural responses elicited to observing the actions of others

Monkey electrophysiological and human neuroimaging studies indicate the exi stence of specialized neural systems for the perception and execution of ac tions. To date, the dynamics of these neural systems in humans have not bee n well studied. Here, we investigated the spatial and temporal behavior of human neural responses elicited to viewing motion of the face, hand, and bo dy. Scalp event-related potentials (ERPs) were recorded in 20 participants viewing videotaped mouth (opening, closing), hand (closing, opening), and b ody stepping (forward, backward) movements. ERP peak differences within the movements of each body part were compared using topographical maps of volt age, voltage difference, and Student's t-test at ERP peak latencies. Predom inantly temporoparietal negative ERPs occurred to motion of all body parts within 200 ms postmovement onset. Hand closure elicited a significantly gre ater negativity than opening, particularly in the left hemisphere. Vertex p ositive ERPs within 300 ms postmovement onset were elicited to hand and bod y motion. A significantly greater positivity occurred for the body stepping forward relative to stepping backward. The ERP topography was consistent w ith observed activation foci in human neuroimaging studies. Our data indica te that the neural activity of a system dedicated to the perception of high -level motion stimuli can rapidly differentiate between movements across an d within body parts.