Apathy and impulsivity in neurological and psychiatric disorders

Apathy and impulsivity are debilitating syndromes of motivation that are common across neurological and psychiatric disorders. Both are associated with pathology within well described fronto-striatal networks where dopaminergic neurons play an important role in regulating motivated behavior. In this chapter, we investigate whether dopaminergic dysfunction within this network is associated with either apathetic or impulsive behavior. We focus on patients with Parkinson's disease and schizophrenia, investigating a wide range of behavioral and neuroimaging studies. Current findings suggest that both apathy and impulsivity are associated with altered responsiveness to rewards during decision-making and altered function within fronto-striatal networks. While dopaminergic therapy also alters reward sensitivity, there are instances where the effects of apathy and/or impulsivity on this metric are independent of—and extend beyond—dopaminergic tone. This suggests a more nuanced relationship between fronto-striatal dopamine and human motivation syndromes that warrants further investigation.