Depletion of dopamine in a circumscribed area of association cortex in rhesus monkeys produces an impairment in spatial delayed alternation performance nearly as severe as that caused by surgical ablation of the same area. This behavioral deficit can be pharmacologically reversed with dopamine agonists such as L-dopa and apomorphine. These data provide direct evidence that dopamine plays an important role in a specific cortical function.

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The present investigation addresses itself to the question of whether the delay, the spatial features, or a combination of the two is the critical factor giving rise to the delayed-alternation deficit produced by ablation of the principal sulcus in the monkey. The effects of fractional prefrontal lesions were compared on delayed response and place reversal, two tests which involve both factors and on go, no-go alternation, which involves only the delay factor. The present results together with those from a previous study indicate that lesions of the dorsolateral prefrontal cortex produce two dissociable disorders, the one classically associated with the frontal lobes having its cortical focus in the principal sulcus, and the other, as yet poorly understood, with its focus in the arcuate sulcus. The classical disorder appears to be related to the combination of mnemonic and spatial factors rather than to either factor alone.

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