Microstimulation reveals specialized subregions for different complex movements in posterior parietal cortex of prosimian galagos

Posterior parietal cortex of prosimian galagos consists of a caudal half characterized by connections with visual cortex and a rostral half connected with motor, premotor, and visuomotor areas of frontal cortex. When 500-ms trains of electrical pulses were used to stimulate microelectrode sites throughout posterior parietal cortex, movements were elicited only from the rostral half. The movement zone reflected an overall pattern of somatotopy, from eye and face movements most ventrally to hindlimb movements most dorsally. In addition, subregions or zones of this movement cortex seemed to be devoted to components of different, ethologically significant behaviors. Thus, microstimulation within separate zones of cortex elicited reaching, hand-to-mouth, defensive, or aggressive movements. The finding of similar classes of elicited movement patterns from frontal and more recently intraparietal cortex of macaques suggests that multiareal circuits for biologically significant behaviors are components of all primate brains and that these circuits can be activated by long trains of current pulses at rostral locations in posterior parietal cortex.