NERVE INNERVATION OF THE HAND AND ASSOCIATED NERVE DOMINANCE AGGREGATES IN THE SOMATOSENSORY CORTEX OF A PRIMATE (SQUIRREL-MONKEY)

The cutaneous innervation territories of the median, ulnar, and radial nerves to the hand were determined from neurophysiological recordings of peripheral mechanoreceptor axons in adult squirrel monkeys. These territories were then related to cutaneous receptive fields of cortica l area 3b neurons to determine how low-threshold inputs from each hand nerve map onto the primary somatosensory cortex. The results indicate that mechanoreceptor axons in each nerve innervate a continuous skin territory covering about 40% of the hand surface. The total territory of each nerve contains subregions of skin that are either autonomously innervated by that nerve or that receive overlapping innervation from more than one nerve. The autonomous, overlap, and total territories o f each nerve are relatively constant from hand to hand. In the area 3b cortex, low-threshold afferents from each nerve provide inputs to agg regates of cortical neurons. The cortical aggregates relating to the m edian and ulnar nerves are arranged as continuous, rostrocaudally orie nted bands, whereas aggregates relating to the radial nerve are discon tinuous and more patchlike. Similar patterns of bands and patches, and similar compression ratios of skin/cortical area, are seen across dif ferent monkeys. These findings demonstrate that the primary somatosens ory cortex of normal adult primates contains bands or patches of neuro ns that are dominantly activated by low-threshold inputs from specific hand nerves. This approach of delineating nerve territories and their related cortical dominance aggregates provides a useful means of anal yzing cortical images of nerves and of quantitating peripheral and cen tral patterns of deprivation after nerve injury. (C) 1993 Wiley-Liss, Inc.