Function of the 'direct' and 'indirect' pathways of the basal ganglia motor loop: evidence from reciprocal aiming movements in Parkinson's disease.

The purpose of this study was to test the validity of a neural-network model of the basal ganglia developed by Bischoff and colleagues (A. Bischoff, Modeling the basal ganglia in the control of arm movements (Doctoral dissertation, University of Southern California, 1998). Dissertation Abstr. Int. 59-08B (1998) 3924, 0208; A. Bischoff, M.A. Arbib, Modeling the role of basal ganglia and supplementary motor areas in sequential arm movements, Abstr. Soc. Neurosci. 23 (1997) 466; A. Bischoff, M.A. Arbib, C.J. Winstein, Modeling the role of the basal ganglia in reciprocal aiming task, Proceedings of the Fourth Annual Joint Symposium on Neural Computation, University of Southern California, Los Angeles, 7, 1997, pp. 20-27), and to examine the effects of levodopa on aiming movement performance. Findings confirm the model predictions for repetitive aiming movements. Individuals with late stage Parkinson's disease demonstrated longer movement times and longer pauses between aiming sequences compared to controls. Levodopa only slightly improved bradykinesia but not akinesia in these patients.