Identifying the Basic Dimensions of Medication-Triggered Impulsive Compulsive Behaviours in Parkinson's Disease.

Background: This review article integrates findings from published behavioural and neuroimaging studies of impulsive-compulsive behaviours (ICBs) in Parkinson's disease, with the aim of identifying the basic correlates of these problematic and distressing behaviours. The underlying premise is that for any feature to be a reliable marker of ICBs, it should be evident across multiple levels of analyses. When changes are evident only at one level, but not in the others, their reliability as indicators of ICBs should be questioned.

Summary: To this end, we draw on the conclusions from three published systematic reviews of dopamine metabolic processes in the striatum, functional magnetic resonance imaging and cognitive, affective, and motivational assessments of medicated Parkinson's patients with and without ICBs (ICB+ and ICB-, respectively). The key findings are as follows: ICB+ showed abnormal dopaminergic of the striatum, including the brain network supporting reward processing. Fronto-striatal connectivity was also reduced. These findings are consistent with the broader evidence of psychological dysfunction, evident on assessments of cognitive control (goal-driven behaviour, impulsivity), reward-driven decision-making (temporal discounting, gambling), and elevated rates of self-report negative affect (anxiety, depression, anhedonia). The implications of these findings are discussed with reference to the research domain criteria and, relatedly, directions for future research.

Key messages: The identification of markers of ICB that allow early diagnosis, monitoring, and optimisation of therapy is an ambitious goal. And whilst we have pulled together a number of convergent findings identified using different paradigms, we are still some distance off understanding the mechanism(s) that increase vulnerability to ICB. It is our hope that this review spurs future studies to further investigate the interaction between motivation and cognition with the twin aims of identifying markers of ICB that have both clinical utility and function as outcome measures in therapeutic clinical trials.