Dopaminergic effects on cognitive performance in patients with Parkinson's disease.

A group of twelve patients with idiopathic Parkinson's disease was assessed both on and off L-Dopa medication on a range of tests of cognitive performance. Withdrawal of L-Dopa produced impairments in tests sensitive to frontal lobe dysfunction such as verbal fluency and the Tower of London task. Another test of frontal lobe function, the Wisconsin Card Sorting Test, was not affected in the absence of L-Dopa. Memory functions such as short-term span and verbal paired associate memory were not impaired by L-Dopa withdrawal. The results suggest that some of the cognitive impairments observed in Parkinson's disease, namely frontal lobe deficits, are related to a loss of central dopaminergic function.