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Spike activity was recorded from three zones of the putamen in monkeys trained to bimanual operant activity during performance of an alternative spatial selection task. Neuron responses were analyzed using the following criteria: a) differentiation of the side providing reinforcement (differentiating/non-differentiating responses); b) response duration (tonic/phasic); c) response laterality (contralateral/ipsilateral hemispheres); d) baseline activity frequency. The differentiating activity of cells was found to show the closest correlation with behavioral aspects of the program, particularly the tonic part and, even more so, contralateral tonic responses. It is suggested that differentiating activity, as opposed to non-differentiating activity, is less a reflection of the morphological and neurochemical characteristics of the neural elements of the putamen than of their functional homogeneity in relation to external determinants of behavior.