Dopamine-Dependent Frontostriatal Planning Deficits in Early Parkinson's Disease

Three groups of medicated and nonmedicated patients at different stages of Parkinson's disease and a group of neurosurgical patients with localized frontal lobe excisions were assessed on 2 novel tests of planning and spatial working memory. Results demonstrate that, like other tests of frontal lobe dysfunction, planning and spatial working memory are vulnerable in nonmedicated patients with mild Parkinson's disease and suggest that certain aspects of the planning impairment in these patients may be ameliorated by dopaminergic therapy. Specifically, with medication there was an improvement in accuracy of planning, but not in latency, in a series of problems based on the Tower of London test of planning. The results in terms of the frontostriatal, dopamine-dependent nature of some of the cognitive deficits found in early Parkinson's disease versus the apparent dopamine-independent nature of deficits in other cognitive processes are discussed. As may be expected from the intimate relation that exists between the basal ganglia and the frontal cortex (Alexander, Delong, & Strick, 1986), recent neuropsychological evidence suggests a substantial role for frontal lobe dysfunction in the cognitive profile of patients with Parkinson's disease (Bowen, Kamienny, Burns, & Yahr, 1975; Canavan et al., 1989; Downes et al., 1989; Lees & Smith, 1983; Owen et al., 1992; Scatton, Javoy-Agid, Rouquier, Dubois, & Agid, 1983; Taylor, SaintCyr, & Lang, 1986). Although few direct comparisons have been made between patients with frontal lobe damage and patients with Parkinson's disease, similar patterns of cognitive impairment have been observed in the two groups in many studies. For example, deficits on the Wisconsin Card Sorting Task, a commonly used clinical index of frontal lobe damage