Pericruciate cortex unit activity during intentional movement. Effect of subcortical electrical stimulation

Extracellular unitary activity of pericruciate cortex neurons (CPCns) was recorded in cats performing a learned flexion--extension movement of the contralateral forearm. The present report concerns solely those cells showing firing changes on electrical stimulation of nucleus medialis dorsalis thalami (DM). These CPCns responding to DM stimulation (CPCdmns) were classified as either pyramidal tract or non-pyramidal tract neurons (CPCdm PTns, CPCdm non-PTns) by antidromic activation of the medullar pyramid. In addition, convergence of DM and other subcortical structures (lateral hypothalamus HL, basal amygdala AB, and dorsal amygdala AD) on CPCdmns was tested by means of single and paired electrical stimulation. On the bases of the obtained data, CPCdmns had been grouped in the following different types. Type I: thirty-two neurons activated by stimulation of all the studied subcortical structures. All these cells are PT neurons and 20 of them (62.5%) are task-related, showing firing frequency increase before movement onset. Type II: forty-six neurons also activated by stimulation of all subcortical structures. All are non-PT cells and 17 of them (36.9%) are task-related, showing firing decrease or firing arrest at movement onset. Type III: twenty-one neurons activated exclusively by DM stimulation (and therefore non-PT cells). Four of them (19%) being task-related, and showing firing increase after movement onset. Type IV: twenty neurons responding exclusively to DM stimulation with firing frequency increase frequency decrease. None of them was movement-related. It is concluded that the cat's CPC agranular cortex receives effective inputs from such subcortical structures as DM, AB, AD and HL and that these subcortical structures play an important role in the regulation of motorcortical cell activity.