The genitals and gluteal skin are represented lateral to the foot in anterior parietal somatosensory cortex of macaques.

Detailed electrophysiological maps of the representations of trunk and adjacent body parts in area 3b and area 1 of somatosensory cortex were obtained in three macaque monkeys (Macaca mulatta and Macaca radiata) of either sex. A total of 211 microelectrode penetrations 250-300 microm apart resulted in 1,190 recording sites. During penetrations deep into the posterior bank of the central sulcus, recordings were made every 300 microm to depths of 6-7 mm until sites unresponsive to somatic stimuli were reached. Cortex was later cut parasagittally and sections were stained for cytochrome oxidase (CO) or Nissl substance. Contrary to expectations from earlier reports, the genitalia were represented lateral to the representations of the foot in cortex along the area 3b/1 border. The gluteal skin including the gluteal pads and the base of the tail were also represented in this section of cortex. Only a small region of cortex was devoted to the genitalia, and neurons in this cortex had receptive fields that were large and typically included skin of the inner thigh and belly. The lower, middle and upper trunk were represented more laterally, followed by the neck, upper head and arm. The receptive fields on the trunk were roughly the same size as those for the middle and lower trunk and slightly smaller on the upper trunk.