Reduction during movement of the evoked potentials recorded along the extralemniscal pathways of the cat

Five cats were trained to press a pedal or to stay still. Electrical stimulation was delivered to the skin of the forelimb when the cats stayed still and when they pressed the lever. Gross evoked potentials (EPs) were recorded over the suprasylvian gyrus (ASSG) and in two subcortical non-specific structures: the bulbar nucleus gingantocellularis (NGC) and the centrum medianum of the thalamus (CM). EPs recorded in NGC and over the ASSG showed an early and a late component. In the CM only one component was consistently present in all animals. During the conditioned movement, the EP was reduced in NGC, in CM and over the ASSG. This diminution was statistically significant for the cortical (early and late waves) and the thalamic responses; at the bulbar level the late wave only was diminished. These results are in agreement with the reduction of the cutaneous volley conducted by the lemniscal pathways. The origin and degree of depression of the early and late components are discussed.