9 When the spark goes out: the neurology of apathy and motivation

Abstract

Disorders of motivation are common across brain disorders. Clinicians frequently encounter pathological apathy across a range of conditions, including many neurodegenerative conditions such as small cerebrovascular disease, Parkinsons and Alzheimers disease. It is now becoming understood that apathy has a poor prognosis for long-term functional and cognitive outcome. Unfortunately, we understand very little about the mechanisms underlying the syndrome.In this talk, I shall put forward a conceptual framework with which we can begin to understand apathy by considering the processes that normally underlie motivated, goal- directed behavior. In particular Ill focus on the ability to generate options for behavior and effort-based decision making for rewards. Recent studies of the latter have been particularly revealing in both healthy people and neurological patient populations.Several lines of evidence suggest that when we make decisions about how much effort we might invest in actions, we weigh up the costs involved for the potential rewards to be obtained. Functional imaging in healthy people reveals both medial frontal and basal ganglia involvement when individuals make such decisions. In patients with apathy, this evaluation is altered. Apathetic patients show blunted sensitivity to rewards and less inclination to invest effort for low rewards than healthy individuals. Some evidence shows that these factors can be improved by dopaminergic medication. The findings support the view that it might be possible to provide a mechanistic account of the syndrome of apathy which might lead to treatments for the disorder.