Probabilistic learning and reversal deficits in patients with Parkinson's disease or frontal or temporal lobe lesions: possible adverse effects of dopaminergic medication

Three groups of patients with Parkinson's disease (PD) - mild, unmedicated (UPD), mild, medicated (MPD) and severe, medicated (SPT) - and patients wit h lesions of the frontal lobe (FLL) or temporal lobe (TLL) were compared wi th matched controls on the learning and reversal of probabilistic ic and tw o-pair concurrent colour discriminations. Both of the cortical lesion group s showed reversal deficits, with no increase in perseverative responding. T he UPD group, although impaired on a spatial recognition task, showed intac t discrimination learning and reversal; the MPD and SPD patients showed non -perseverative reversal impairments on both reversal tasks. Two hypotheses - based on disease severity and possible deleterious effects of medication - are offered to explain the reversal impairments of the PD patients and th e results are discussed in terms of the role of dopamine in reward-based le arning. (C) 2000 Elsevier Science Ltd. All rights reserved.