Altered N400 Congruity Effects in Parkinson’s Disease without Dementia

The N400 congruity effect (event-related brain potential (ERP) 300–500 ms poststimulus onset to contextually incongruent minus congruent words) generally shows a linear amplitude decrease with normal aging, and an even greater decrease in Alzheimer's dementia. As little is known about N400 effects in Parkinson's disease (PD), we recorded ERPs in 11 elderly patients with PD (without dementia, mean age = 66 years) during antonymic and category verification. Nondemented PD patients exhibited larger N400 congruity effects than their age-matched controls, consistent with reports of behavioral hyperpriming and possibly insufficient inhibition of irrelevant semantic information and/or greater target activation. It is also consistent with abnormally heavy reliance in PD on external cues. These findings implicate abnormal dopaminergic signaling (e.g., frontostriatal and/or mesocortical circuits) in PD, despite l -dopa therapy.