Short-latency projections to the cat's cerebral cortex from skin and muscle afferents in the contralateral forelimb.

1. The potentials evoked in the first sensorimotor area on stimulation of muscle and skin nerves in the contralateral forelimb were recorded in preparations with either the dorsal funiculus (DF) or the spinocervical tract (SCT) interrupted.2. The short-latency, surface-positive potentials in these preparations are mediated by the remaining path, either the DF or SCT.3. Cutaneous afferents project through both paths to two discrete areas which correspond to the classical sensory and motor cortices (Fig. 10 A and B). The projection areas are not identical: the DF path seems to activate most effectively the sensory cortex; and the SCT path, most effectively the motor cortex.4. The potentials evoked from cutaneous nerves have a similar latency in the two areas. On stimulation of the superficial radial nerve the latency was about 4.5 msec in preparations with intact DF, and about 5.3 msec in preparations with intact SCT.5. High threshold muscle afferents project to the same areas as the cutaneous afferents.6. Group I muscle afferents project, exclusively through the DF path, to an area distinct from the two cutaneous projection areas (Fig. 10C). It occupies a caudal part of the motor cortex and an intermediate zone between the sensory and motor cortices.7. The projection areas are compared with the recent cytoarchitectonic map of Hassler & Muhs-Clement (1964) (Fig. 10D).8. It is suggested that the afferent projections to the motor cortex and the intermediate zone are used in the integration of movements elicited from the cortex. The general similarity in the organization of afferent paths to the motor cortex and the cerebellum is pointed out.