Disturbances in higher function in Parkinson's disease.

The most striking of the cognitive deficits in Parkinson's disease is 'subcortical dementia', which is similar to the cognitive deficits caused by frontal lobe damage. Of the several causes of the cognitive deficits in Parkinson's disease, the most interesting theoretical mechanism is the dysfunction of the cortical-basal ganglionic circuits connecting the frontal lobe and the basal ganglia. As the activity of these circuits can be modulated at the striatum by the nigrostriatal dopaminergic system, cognitive function can be influenced by the pathological change in the substantia nigra in Parkinson's disease. As a result of the dysfunction of this system, disturbances of memory, attention, and executive function occur. Our study found that the dopaminergic system plays a role in the disturbance of the set-shifting ability in Parkinson's disease.