Visual motion responses of neurons in the caudal area pe of macaque monkeys.
Area PE of macaques has traditionally been considered a somatosensory association cortex. Recent studies, however, suggest that neurons of this and neighboring areas are involved in the visual control of movement, especially arm movement. We investigated the neuronal sensitivity to local visual stimuli of this region by recording neuronal activity in two behaving macaque monkeys trained in a simple visual fixation task. Recordings were performed from the dorsal surface of the caudal pole of the superior parietal lobule (SPL). Classical receptive fields (RFs) were mapped by using conventional static or moving luminous figures. We found that many neurons in this area were selectively activated by moving visual stimuli. Cell responses were tuned to the movement direction. RFs were usually large; their mean surface covered some 30 x 30 degrees of the visual field. The fovea was often included into RF, in many cases it was along a RF side. The center of RFs was mainly located in the contralateral hemifield, although RFs having the center ipsilaterally sited were also found. No evident retinotopy was found. Visual neurons were especially concentrated in a region of the SPL likely corresponding to area PEc. These results suggest that the caudal part of area PE contains neuronal populations specifically signaling local visual motion, possibly encoding the direction of moving objects. These signals might well be suited for sensorimotor integration mechanisms aimed at motor acts.