Motivational engagement in Parkinson's disease: Preparation for motivated action

Abstract

The current study investigated whether motivational dysfunction in Parkinson's patients is related to a deficit in preparing for motivated behavior. Based on previous studies, it was hypothesized that PD patients would show reduced preparation for action specifically when faced with threat (of loss) and that reduced action preparation would relate to self-report of apathy symptoms. The study measured an electrocortical correlate of preparation for action (CNV amplitude) in PD patients and healthy controls, as well as defensive and appetitive activation during emotional perception (LPP amplitude). The sample included 18 non-demented PD patients (tested on dopaminergic medications) and 15 healthy controls who responded as quickly as possible to cues signaling threat of loss or reward, in which the speed of the response determined the outcome. Results indicated that, whereas PD patients showed similar enhanced action preparation with the addition of incentives to controls, PD patients showed generally reduced action preparation, evidenced by reduced CNV amplitude overall. Results suggest that PD patients may have behavioral issues due to globally impaired action preparation but that this deficit is not emotion-specific, and movement preparation may be aided by incentive in PD patients.

Keywords: CNV; Incentive; LPP; Motivation; Motor preparation; Parkinson's.

Fig. 1

Top: Illustration of threat of loss, reward, and neutral preparation for action trials. Bottom: Schematic of experimental design. On a preparation for action trial, the warning cue was presented for 3 s, followed by a red screen which indicated that the participant should press the space bar as fast as possible. The participant then received feedback about whether money was won, lost, or neither, based on whether the reaction time on that trial was faster than an individual’s 90th percentile reaction time cut-off. Affective and neutral pictures were pseudo-randomized with preparation for action trials. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

A: Topographies showing average changes in voltage at the scalp for Parkinson patients (top) and healthy controls (bottom) during the CNV time window, from 2000 to 3000 ms after cue onset during preparation for action trials. B: Event-related potentials during the presentation of reward, threat, and neutral incentive motivation cues, prior to the motor response for a centroparietal sensor group. Grayed background indicates time window for ERP analysis. Effect of incentive motivation on CNV amplitude was significant in both Parkinson and Control groups. C: The contingent negative variation, measured at a centro-parietal sensor group, during the last second prior to the motor response. Grayed background indicates time window for ERP analysis. PD patients showed reduced late CNV amplitude compared to controls. D: Relationship between disease duration and reduction in reaction time during reward (compared to neutral) trials. Note that reaction times have been back-transformed from the log transformation applied to raw reaction time data for analyses, and are thus presented in milliseconds.

Fig. 3

A: Topographies showing average changes in voltage for Parkinson patients (top) and healthy controls (bottom) during unpleasant, neutral, and pleasant picture viewing in the LPP time window, from defined as 500–1000 ms following picture onset, during. B: Event-related potentials during the presentation of pleasant, unpleasant, and neutral pictures, at central-posterior sensor group. Grayed background indicates time window for ERP analysis. PD patients showed enhanced LPP during pleasant compared to unpleasant picture viewing, whereas controls do not.