Parkinson's disease: a conceptualization of neuropsychological deficits within an information-processing framework.

Parkinson's disease patients are frequently impaired in a variety of neuropsychological tasks involving memory, perceptual motor performance and cognitive flexibility. Although various theories have been forwarded to explain specific impairments, few attempts have been made to account for all the deficits within a single theoretical framework. Furthermore, the frequent occurrence of dementia, the adverse side effects of medication and the motor symptoms of the disease tend to interfere with neuropsychological performance. This has hindered the clear delineation of the neuropsychological profile of Parkinsonian patients. The present paper examines the evidence for intellectual deficits in non-demented Parkinson's disease patients. A number of problems inherent in cognitive research on Parkinson's disease are discussed. The contribution of dementia, motor symptom severity and medication in the expression of these intellectual impairments is examined. It is suggested that many of the neuropsychological deficits described in Parkinson's disease may result from a common underlying deficit in some aspect of information processing. Although it is not possible to pinpoint the precise mechanism(s) involved on the basis of the available evidence, several possibilities are suggested by cognitive and electrophysiological data.