“Facilitation” and “Reversal of Response” of Neurones in the Cerebral Cortex

Abstract

IN the course of experiments in which movements were elicited by direct electrical stimulation of the cerebral cortex, Graham-Brown^1–4 and Sherrington⁵ found that, after each train of stimuli, there were prolonged changes in the excitability of the cortex. They showed that the motor responses of forelimb muscles in primates, even though elicited by identical cortical stimuli, could be extremely variable. Two of the phenomena they described in detail (see also Lilly⁶) were “facilitation” (the increased motor response resulting from a second train of stimuli when it was applied within 20 s after the first train) and “reversal of response” (when repeated, identical stimulation of the same cortical point elicited flexion instead of extension, or vice versa).