Defensive movements evoked by air puff in monkeys.

Electrical stimulation of two connected cortical areas in the monkey brain, the ventral intraparietal area (VIP) in the intraparietal sulcus and the polysensory zone (PZ) in the precentral gyrus, evokes a specific set of movements. In one interpretation, these movements correspond to those typically used to defend the body from objects that are near, approaching, or touching the skin. The present study examined the movements evoked by a puff of air aimed at various locations on the face and body of fascicularis monkeys to compare them to the movements evoked by stimulation of VIP and PZ. The air-puff-evoked movements included a movement of the eyes from any initial position toward a central region and a variety of stereotyped facial, shoulder, head, and arm movements. These movements were similar to those reported on stimulation of VIP and PZ. One difference between the air-puff-evoked movements and those evoked by stimulation of VIP and PZ is that the air puff evoked an initial startle response (a bilaterally symmetric spike in muscle activity) followed by a more sustained, lateralized response, specific to the site of the air puff. In contrast, stimulation of VIP and PZ evoked mainly a sustained, lateralized response, specific to the site of the receptive fields of the stimulated neurons. We speculate that VIP and PZ may contribute to the control of defensive movements, but that they may emphasize the more spatially specific reactions that occur after startle.