DELAYED-RESPONSE TASKS IN BASAL GANGLIA LESIONS IN MAN - FURTHER EVIDENCE FOR A STRIATO-FRONTAL COOPERATION IN BEHAVIORAL ADAPTATION

To determine the respective contribution of the subcortical structures and the prefrontal cortex in behavioural adaptation, we applied the d elayed response paradigm, considered as a functional marker of the dor solateral region of the prefrontal cortex, to patients with striatal d ysfunction: Parkinson's disease (n = 27), progressive supranuclear pal sy (n = 20); to patients with prefrontal lesions (n = 10) and to norma l control subjects (n = 24). The performance of each group was compare d in four experiments: a delayed response task in which the correct an swer was previously indicated by an explicit cue (externally guided ta sk); delayed alternation and non-alternation tasks coupled with a dela yed reversal task in which the patient had to discover the rule by him self in the absence of explicit cues (internally driven tasks). All gr oups of patients showed a short-term spatial representational memory d eficit in the externally guided situation. Patients with striatal dysf unction showed difficulties in re-engaging attention on a new programm e and in maintaining it. However, they did not express the spontaneous tendency to alternate nor the severe difficulties in disengaging from a previous pattern of response demonstrated by patients with prefront al lesions. These results validate the concept of a striato-frontal fu nctional system in humans and suggest the existence of two different l evels of behavioural organization: elaboration of new programmes of be haviour in association with inhibition of previously established ones, that might be under frontal lobe control; maintenance of the new prog ramme until the action has been accomplished and automatization for a routine utilization, that might be under control of the striatum. Copy right (C) 1996 Elsevier Science Ltd.