A single dose of L-DOPA changes perceptual experiences and decreases latent inhibition in Parkinson's disease.

Despite the well-known neuropsychiatric side effects of dopaminergic medications, the possible subjective psychotomimetic effects of a single dose of L-DOPA in newly diagnosed, drug-naïve patients with Parkinson's disease (PD) are not known. To investigate this question, we used a visual search task for latent inhibition (LI), the Community Assessment of Psychic Experiences (CAPE) scale, and visual analog scales for psychotomimetic effects (perception, relaxation, and dysphoria) in 28 de novo PD patients before (off) and after (on) the adminstration of L-DOPA and in 25 matched healthy control individuals. Results revealed increased LI in PD-off and decreased LI in PD-on relative to the control subjects. After the administration of L-DOPA, we observed a significant decline in LI in PD. L-DOPA also enhanced perceptual experiences (changes in subjective feelings in thinking, time perception, and mental "highness"). Greater reduction in LI was associated with enhanced perceptual experiences. These results suggest that a single dose of L-DOPA has a significant psychotomimetic effect, which is associated with decreased LI, a behavioral marker of psychosis-like experiences.