Human neural responses elicited to observing the actions of others.

Monkey electrophysiological and human neuroimaging studies indicate the existence of specialized neural systems for the perception and execution of actions. To date, the dynamics of these neural systems in humans have not been well studied. Here, we investigated the spatial and temporal behavior of human neural responses elicited to viewing motion of the face, hand, and body. Scalp event-related potentials (ERPs) were recorded in 20 participants viewing videotaped mouth (opening, closing), hand (closing, opening), and body stepping (forward, backward) movements. ERP peak differences within the movements of each body part were compared using topographical maps of voltage, voltage difference, and Student's t-test at ERP peak latencies. Predominantly temporoparietal negative ERPs occurred to motion of all body parts within 200 ms postmovement onset. Hand closure elicited a significantly greater negativity than opening, particularly in the left hemisphere. Vertex positive ERPs within 300 ms postmovement onset were elicited to hand and body motion. A significantly greater positivity occurred for the body stepping forward relative to stepping backward. The ERP topography was consistent with observed activation foci in human neuroimaging studies. Our data indicate that the neural activity of a system dedicated to the perception of high-level motion stimuli can rapidly differentiate between movements across and within body parts.