Afferent properties of periarcuate neurons in macaque monkeys. I. Somatosensory responses.

The afferent properties of single neurons of the periarcuate cortex have been studied in the macaque monkey. Most of the recorded neurons responded to stimuli in one or two sensory modalities and, accordingly, they were classified as somatosensory, visual or bimodal (visual and somatosensory) neurons. Visual neurons were located rostral to the arcuate sulcus, whereas the somatosensory and the bimodal neurons were found predominantly caudal to this sulcus. Somatosensory neurons (n = 102) and bimodal neurons (n = 69) had identical somatic afferent properties. They were subdivided into 'tactile' neurons, 'joint' neurons and 'tactile and joint' neurons. 'Tactile' neurons (70%) had their receptive fields formed either by one or by two or more spatially separated responding areas. The parts of the body most represented were the hands and the mouth. 'Joint' neurons (10%) were activated by the rotation of one or, more often, of two or more articulations. The movement of the hand towards the mouth was the most frequently represented movement. 'Tactile and joint' neurons (20%) responded to both tactile and joint stimulation having receptive field locations and properties like those of the other two classes of neurons. Some 'joint' and 'tactile and joint' neurons had summing properties, i.e. their response to tactile or joint stimulation was conditional upon a simultaneous stimulation of another articulation. The data are interpreted as evidence in favor of the existence of an area in the agranular cortex that organizes the mouth and the hand to mouth movements.