Motivational disturbances and cognitive effort-based decision-making in Parkinson's disease

Motivational disturbances, such as apathy and impulse control disorders (ICDs), frequently co-occur in patients with Parkinson's disease (PD). The assessment of these motivational disturbances has proven to be challenging due the absence of validated objective behavioral measures for evaluating motivation in older adults. This scenario may contribute to underdiagnosis. The present study aimed to investigate the clinical utility of a modified version of an existing effort-based decision-making task which required cognitive (e.g., working memory) instead of physical (e.g., finger tapping) effort.

Ninety-five non-demented individuals (45-85 years of age) with idiopathic PD completed a cognitive screening measure, self-report questionnaires, and a cognitive adaptation of the Effort Expenditure for Rewards Task (COG-EEfRT), which is a multi-trial game where a participant can choose whether to expend greater effort for larger rewards which vary in magnitude and probability. Patients were classified as having clinically significant symptoms of apathy and/or an ICD based on recommended cut-off scores on the Apathy Scale (AS) and Questionnaire for Impulse Control Disorders in Parkinson's Disease - Rating Scale (QUIP-RS). The methodological cutoffs defined two groups: Apathy (36.8 %), and ICD (48.4 %).

The level of effort expended by patients significantly predicted apathy and ICD status with high accuracy (88.2 % and 82.4 %, respectively), above and beyond age, levodopa equivalent dose and self-report measures of motivation. Additionally, we found that greater symptoms of apathy and ICD (i.e., negative urgency) were significantly correlated with patients choosing to expend greater effort. This result varied based on reward probability and outcome.

We offer preliminary evidence suggesting the clinical utility of the COG-EEfRT for identifying and quantifying motivational disturbances in PD. Additionally, anticipatory anhedonia and impulsive traits may be important predictors of cognitive effort-based decision-making. Compared to tasks requiring physical effort, the COG-EEfRT may be a more suitable tool for PD and perhaps for people with motor impairment.