Microstimulation of Precentral Cortex with Chronically Implanted Microelectrodes

Both excitation and inhibition of electromyographic (EMG) activity were observed in proximal as well as distal musculature. The activation pattern from a given electrode usually remained constant for many days. Changes in the activation pattern, when they did occur, were probably due to movements of the electrode. Individual proximal muscles were activated from a larger region of cortex than were individual distal muscles. The latency for contraction of a proximal muscle varied with intracortical stimulus site, indicating different projection strengths from the different sites or different synaptic pathways. Sensory-evoked neural activity, recorded with the stimulating electrode, usually was from the same region as the muscle activated by ICMS. Operant conditioning of neuronal firing patterns, recorded from the stimulating electrode, resulted in the monkey activating the same muscle as was activated by ICMS. These results indicate a topographically related input-output organization of the precentral gyrus.