Inhibition of spinocervical tract discharges from localized areas of the sensorimotor cortex in the cat.

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Abstract
Intracortical microstimulation (ICMS) was applied within the sensorimotor cortex of cats anesthetized with chloralose. The effects of the ICMS were examined on the number of impulses in spinocervical tract (SCT) cells (recorded extracellularly in the contralateral lumbosacral spinal cord) evoked by peripheral stimulation. Inhibition of SCT discharges was produced by ICMS in 2 distinct regions of the sensorimotor cortex. One inhibitory region was in part of cytoarchitectonic area 4.gamma. in the upper bank of the cruciate sulcus. It sometimes extended caudally into area 4.delta., medially into area 3a and/or rostrally into the part of area 4.gamma. on the caudal lip of the cruciate sulcus. The other inhibitory region was in the medial part of the posterior sigmoid gyrus and included parts of areas 3a, 3b, 1, 5a and 5b. Most inhibitory sites were in cortical layers III, V and VI. No regions were found in which ICMS consistently caused facilitation of SCT discharges.