Dr Matthew Apps, University of Oxford

Opportunities, costs and dopamine: A computational neurology approach to apathy and fatigue in health and Parkinson’s Disease

Motivation – the willingness to suffer a cost to obtain a benefit – is crucial for successful, adaptive behaviour. Impairments to motivation such as apathy – a reduction in goal-directed behaviour – and fatigue – a feeling of exhaustion inhibiting the initiation of actions – are some of the most common and debilitating symptoms in neurological conditions including Parkinson’s Disease (PD).

Whilst most research probing such motivational impairments has used self-report, recent accounts have suggested that amotivation in PD is linked to a heightened sensitivity to costs, related to a reduction of the efficacy of dopaminergic systems. However, such accounts assume that the processing of costs is static. Yet the willingness to overcome a cost changes both over time, and as the environment changes, with theoretical accounts linking such adaptable behaviour to dopaminergic function. Here, I examine whether apathy and fatigue in PD are linked not to a heightened sensitivity to costs per se, but to how costs are processed in changing environments.

I will present two novel tasks and computational frameworks that probe (i) how motivation changes over time as a function of the history of effort costs (motivational fatigue) and (ii) how changes in the environment influence processing of the cost of “moving on” to greener pastures (foraging). Across a range of studies I highlight the utility of these frameworks for probing both the mechanisms underlying amotivation in healthy people and for testing long-standing theories of dopaminergic function. Moreover, I show that dopaminergic dysfunction provides the link between computational signatures of ‘motivational fatigue’ and ‘foraging’, and heightened fatigue and apathy in PD.

Keywords: contagion, social identity, social psychology, crowd behaviour