Cognitive impairment in Parkinson's disease.

Neuropsychologic studies on Parkinson's disease have shown an impairment of specific cognitive functions and a greater evidence of dementia. Cognitive alterations are related to the gravity of some peculiar motor symptoms of the disease and show a major role of motor disturbances in intellectual disorders. The concept of bradyphrenia and subcortical dementia still seems to be suitable to define the cognitive disorders of Parkinson's disease.