Submodality distribution in sensorimotor cortex of the unanesthetized monkey.

1. Neuronal responses to cutaneous and noncutaneous stimulation were examined in the hindlimb representation of the precentral motor cortex (MI) and the first somatosensory cortex (SI) of unanesthetized monkeys. 2. MI can be divided into two distinct parts of the basis of its afferent input. The rostral part receives predominantly noncutaneous inputs, while the cutaneous input is primarily confined to the caudal part of MI. Thus, a differential distribution of submodality groups exists in the MI cortex. Caudal to MI, area 3a responds mainly to stimulation of noncutaneous receptors, in marked contrast to the caudal part of MI or area 3b. 3. The finding of a differential distribution of cutaneous inputs within MI is of significance a) to hypotheses concerning the role of somatosensory input to the MI cortex, b) to studies that attempt to characterize somatosensory inputs to MI by the proportion of neurons responsive to cutaneous and noncutaneous stimulation, and c) in that they confirm and extend similar findings recently reported for the forelimb representation of an anesthetized New World monkey (43).