Corticofugal cells responding antidromically to stimulation of the cuneate or gracile nuclei of the cat.

Neurones have been identified and precisely located in the Sm 1 and S II cortex of the cat, which responded antidromically to stimulating the contralateral gracile or cuneate nucleus. They were much more numerous in Sm 1, with corticogracile cells medial and corticocuneate cells lateral, many lying buried in the roof of the cruciate or the coronal sulcus. Their position corresponded with cutaneous inputs to the cortex from hind- or fore-parts of the body respectively. Corticogracile cells lay mainly in area 3a with some extension towards area 4. Corticocuneate cells were also mainly in 3a but showed more spread into adjacent rostral and caudal areas. Although some cortical cells project both to these nuclei and to the spinal cord, none were found in the sample tested. The mean latency of antidromic response was much longer (6.9 msec, n = 29) for corticogracile than for corticocuneate cells (3.7 msec, n = 17), the former having a prominent group of slower fibres. The significance of this disparity is discussed in relation to other efferent projections from this region of cortex and a possible relation to the timing of feedback from moving limbs is proposed. The probable complexity of cortical control over these nuclei is emphasized.