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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 (SPD) - and patients with lesions of the frontal lobe (FLL) or temporal lobe (TLL) were compared with matched controls on the learning and reversal of probabilistic and two-pair concurrent colour discriminations. Both of the cortical lesion groups showed reversal deficits, with no increase in perseverative responding. The UPD group, although impaired on a spatial recognition task, showed intact 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 the results are discussed in terms of the role of dopamine in reward-based learning. Neuropsychologia 2000 May 1;38(5):596-612 Swainson R, Rogers RD, Sahakian BJ, Summers BA, Polkey CE, Robbins TW Department of Experimental Psychology, University of Cambridge, Downing Street, Cambridge, UK PMID: 10689037 <http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?uid=10689037&form=6&db=m&Dopt=b> janet paterson 52 now / 41 dx / 37 onset a new voice: http://www.geocities.com/janet313/ 613 256 8340 PO Box 171 Almonte Ontario Canada K0A 1A0