Function of the basal ganglia as revealed by cognitive and motor disorders in Parkinson's disease.

Early Parkinson's disease is taken to be the best human model of disordered basal ganglia function. An experimental study in Parkinsonians with swings in motor response to drug treatment suggests that general cognition is not controlled by dopamine mediated striatal activity. The variety of motor disorders in Parkinson's disease cannot be explained by simple concepts. Although Parkinsonians cannot execute fast ballistic movements, an experimental study shows that they can adopt a predictive motor control strategy. It is argued that simple motor programs are not grossly disturbed in Parkinson's disease. It is concluded that Parkinsonians cannot automatically execute learned motor plans.