To improve our understanding of impaired motivation in Parkinson’s disease (PD), we tested the hypothesis that the neural basis of response to reward and penalty tasks lies within the prefrontal-basal ganglia circuitry.

Reduced motivation is common in PD. PD patients have decreased reactivity to positive (reward) and negative (penalty) signals, which contributes to their motivational disorder. We investigated the neural basis of motivation in patients with PD. 

Participants with PD (mean MOCA=25.5; disease duration=8.2 years; n=27) and demographically-matched controls (NC; mean MOCA=28.4.; n=16) completed a computerized task. We measured reaction time (RT) to press a target key in response to a stimulus presented on a computer screen. To assess motivation, participants were given an amount of money, and money is taken away as a “penalty” if they did not respond more rapidly to the stimulus relative to their previous performance. Participants also perform a “reward” condition where they received money for responding more rapidly. We related RTs on penalty and reward conditionsto volumetric imaging measures in 116 anatomically-defined regions of interest using linear regression models, adjusting for age, sex, total brain volume, and UPDRS-III. 

As expected, PD participants had slower latencies than NC on penalty (t[40]=3.56, p=0.0009) and reward conditions (t[34]=2.79, p=0.008). There were no significant differences in RT between penalty and reward conditions in PD participants. Penalty RT was related to atrophy in the orbitofrontal gyrus, putamen and thalamus. Reward RT was related to atrophy in orbitofrontal gyrus. 

Poor motivation may result from a lack of responsiveness to either reward or negative feedback. Frontal and subcortical regions important for processing this information may have specific roles for motivational functions.