The effect of Parkinson's disease on learning-related slow potentials and emotion

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The dopaminergic reward system is the focus of intensive research because of its relevance to disorders such as addiction, obesity, Parkinson's disease (PD), schizophrenia, and depression. One purpose of the current study was to test whether learning effects on a measure of reward expectancy, the Stimulus-Preceding Negativity (SPN), are dopamine mediated. We compared changes in SPN amplitude across trials as healthy people and people whose dopamine system had been damaged by PD learned a series of probabilistic categorization tasks, in which they were required to find out which of two doors was usually followed by a pleasant picture and which by an unpleasant one. We also assessed dopamine effects in the two groups using a behavioral assay, resting spontaneous eye-blink rate. The second purpose of the study was to test the involvement of dopamine in emotions triggered by positive and negative feedback displays via measures of the late positive potential (LPP), startle blink reflex, post-auricular reflex (PAR), and self-report. Results showed that SPN learning effects seen in the control group were absent in the patient group. These effects did not vary as a function of spontaneous blink rate. Changes in SPN topography suggested that patients might have compensated for impairments in their dopamine-dependent reinforcement learning system by switching to declarative memory. Confirming prior findings, participants with Parkinson's disease were less responsive to negative feedback as indicated by LPP. Patients with low spontaneous blink rate tended to exhibit reduced affective modulation of startle blink. Dopamine plays an important role in both anticipation and receipt of task feedback.