Local, segmental and supraspinal interaction with a dorsolateral spinal cutaneous afferent system

The mutability of the receptive field characteristics of single units in the spinocervical tract of the cat through local, segmental, and supraspinal mechanisms is demonstrated in decerebrate and spinal preparations. Locally, a discrete, nonconcentric, easily fatiguable afferent inhibition, produced by light brushing and cold, is described. Segmentally, strong stimulation of the distal extremities is found to inhibit spontaneous or evoked activity in the spinocervical tract in a variety of patterns which are suggested to be related to reflex progression. Electrical stimulation of the mesencephalic tegmentum, cerebellar nuclei, and a central pontobulbar core is shown to produce a 35% constriction of receptive field area and a generalized decrease in receptive field responsiveness, with the preservation of a small, sensitive, “central” region. The production, by stimulation of the mesencephalic tegmentum, of a negative slow wave occluding a lumbosacral dorsal root potential suggests a presynaptic mechanism for inhibition of activity in the spinocervical tract. The significance of the spinocervical tract in the mechanisms underlying reactivity to “painful” stimulation is discussed.