Patterns of contraction of distal forelimb muscles produced by intracortical stimulation in cats

Abstract

Cortical activation of distal forelimb muscles was examined by using a method of intracortical microstimulation (ICMS) in cats and the following results were obtained. (1) Stimulation of deep cortical layers (laminae V and VI) with trains of stimulating pulses (300/sec, 4–20 μA) could produce sustained contraction of muscles which lasted as long as the ICMS continued (1–3 sec). (2) Stimulation within superficial layers always produced phasic contractions which ended before the termination of the ICMS. (3) Sustained contractions produced by ICMS could be enhanced or reduced by another ICMS delivered into a different part of the cortex. The cortical zone which produced contraction of a muscle was not co-extensive with the zone which inhibited contraction of the antagonist. (4) By properly placing two electrodes within the cortex it was possible to produce simultaneous contraction of antagonistic muscles, i.e., m. extensor digitorum and m. palmaris longus. (5) It is concluded that functional differentiation in motorsensory cortex is accomplished by discrete spatial separation of excitatory and inhibitory zones for each muscle. It is proposed that variety in movement is achieved by activation of various combinations of cortical efferent zones.