Neurobehavioral functioning in Parkinson's disease: The role of basal ganglia-thalamocortical circuit loops in predicting performance.

Abstract

Motivated by current neuroanatomic theories of basal ganglia-thalamocortical circuit loops, this study assessed whether disturbed neuronal outflow from the striatum (occurring in Parkinson's Disease) would lead to circumscribed deficits in cognitive functions thought to be dependent upon the functional integrity of the frontal lobes, the cortical destination of efferent striatal neurons (particularly arising from the caudate nucleus). Further, this study investigated whether such deficits could account for previously reported memory and visuoperceptual difficulties observed in Parkinson's disease (PD) patients. Nineteen nondemented PD patients were matched with 19 normal elderly control subjects on the basis of age, gender, education, and estimated premorbid intelligence. Determination of disease onset and course, severity of motor symptoms, and medication regimen were made on all PD patients. Three categories of neuropsychologic tests were given: (1) tests sensitive to prefrontal cortical dysfunction (the California Sorting Test, a modified version of the Wisconsin Card Sorting Test, temporal ordering, and generative naming), (2) implicit and explicit memory tests (a fragmented pictures test, serial reaction time, continuous recognition memory, and word learning), and (3) visuomotor and perceptual characteristics (including the Block Design and Picture Arrangement subtests of the WAIS-R, Benton Facial Recognition Test, Benton Right-Left Discrimination, and Benton Visual Form Discrimination Test). Consistent with the functional/anatomic hypothesis of subcortical deafferentation of the frontal lobes, the nondemented PD patients demonstrated selective deficits in cognitive functions thought to be dependent upon the functional integrity of the prefrontal cortex; other tasks presumed to rely on other cortical regions and processes (e.g., learning and memory, visuoperceptual and visuoconstructional skills) were not significantly impaired--once performance on the frontally-related tasks was statistically covaried. Results are discussed in terms of the validity of the outflow model in predicting the performance of nondemented PD patients on neuropsychologic measures.