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Abstract
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.