The role of primate putamen neurons in the association of sensory stimuli with movement.

Neuronal activity in the putamen of monkeys was recorded while they performed operantly conditioned body movements. Two categories of neurons were observed. Type I cells had tonic spontaneous discharges and responded to the sensory trigger stimuli for movements with excitation followed by inhibition or with only inhibition. These responses to the trigger stimuli disappeared when the conditioned movement was extinguished. Type II cells were characterized by phasic activity time-locked to the movement. Two subclasses of type II cells were observed. Type IIa cells exhibited phasic discharges before the first movement of a learned, repetitive sequence of arm or orofacial movements that were triggered by the sensory stimuli. Type IIb cells showed phasic activity modulation during each movement in one direction, either flexion or extension, in an unconditioned manner. Activity of the type IIa cells preceded the onset of EMG in prime mover muscles, while most type IIb cells were activated after the EMG had appeared. Thus, in both type I and type IIa cells the activity can be said to be behaviourally contingent. Type I cells show a movement contingent sensory response, and type IIa cells show movement-related activity that is contingent upon the triggering of the movement by a sensory stimulus.