ABSTRACT
Changes in reward circuitry have been studied extensively in substance and behavioural addictions. However, comparatively little is known about the neurobiology underlying impulse control disorders (ICDs) in Parkinson's disease, which show roughly similar risk factors and behavioural presentations to both stimulant and behavioural addictions. ICDs occur in a subset of susceptible patients with Parkinson's disease (PD) following intake of dopamine replacement therapy (DRT). These behavioural disorders often have debilitating effects on a patient's quality of life and increase caregiver burden. This comprehensive review examined findings of 40 neuroimaging studies of ICDs in PD to determine (a) whether there are putative neurobiological commonalities between traditional substance and behavioural addictions and DRT-induced ICD in PD and (b) opportunities for future studies to advance current neurobiological understanding of the phenomenon. Results revealed that strikingly similar (a) deficits in dopaminergic receptor expression, (b) connectivity changes in corticostriatal circuitry and (c) neural responses to cue exposure are observed in both ICDs in PD and addictive disorders. These findings point to the value of adopting a transdiagnostic approach when studying addicted populations and pave the way for demystifying this peculiar, often-devastating phenomenon in PD that has so far proven extremely difficult to treat and predict with any precision.
Subject(s)
Disruptive, Impulse Control, and Conduct Disorders , Parkinson Disease , Disruptive, Impulse Control, and Conduct Disorders/diagnostic imaging , Disruptive, Impulse Control, and Conduct Disorders/etiology , Humans , Magnetic Resonance Imaging , Neurobiology , Parkinson Disease/complications , Parkinson Disease/diagnostic imaging , Parkinson Disease/drug therapy , Quality of LifeABSTRACT
The dorsomedial prefrontal cortex (dmPFC) is a key hub of the 'social brain', but little is known about specific processes supported by this region. Using focal high-definition transcranial direct current stimulation (HD-tDCS) and a social cognitive battery with differing demands on self-other processing, we demonstrate specific involvement of the dmPFC in tasks placing high demands on self-other processing. Specifically, excitatory (anodal) HD-tDCS enhanced the integration of external information into the self for explicit higher-order socio-cognitive tasks across cognitive domains; i.e. visual perspective taking (VPT) and episodic memory. These effects were task specific, as no stimulation effects were found for attributing mental states from the eyes or implicit VPT. Inhibitory (cathodal) HD-tDCS had weaker effects in the opposite direction towards reduced integration of external information into the self. We thus demonstrate for the first time a specific and causal role of the dmPFC in integrating higher-order information from others/external source into that of the self across cognitive domains.
