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Motivation allows us to perform well. A crucial question is, why do we sometimes perform well, but at other times not? One explanation is that it is costly to perform well, but the prospect of reward permits us to pay those costs. Motivation is commonly disrupted in neurological and psychiatric disorders leading to clinical apathy: a higher subjective cost for generating effortful action.

I studied the energisation of action using saccades – simple fast eye movements generated by well-understood circuits in the midbrain. When high rewards are at stake, saccades are earlier, more precise, and more energetic, indicating a higher signal-to-noise ratio in generating movements. This is accompanied by autonomic arousal, as observed by pupil dilatation. Motivational performance improvements  may therefore be controlled at a primitive brainstem level by reward expectation. Rewards can even drive improvements when we are unable to influence the outcome, indicating their simple inflexible nature.

These effects of reward are best explained by introducing a cost for controlling noise into an optimal control framework. How might rewards influence such low-level mechanisms? Variability in the trajectories of saccades suggests that this noise-reduction cost may be due to closed-loop feedback gain in saccade generation. This concept can be extended to cognitive effort. Midbrain dopamine depletion in Parkinson’s disease makes eye movements slower and less sensitive to reward — which in our model is best fit by a higher cost for reducing noise.

 

Sanjay G. Manohar

MA PhD MRCP MBPsS AFHEA

I am an MRC Clinician Scientist at the Nuffield Department of Clinical Neurosciences, University of Oxford, and an Honorary Consultant Neurologist at the John Radcliffe Hospital, a fellow at Lady Margaret Hall, and a fellow of the Software Sustainability Institute. I examine how reward motivates us, using eye movements and pupillometry. My work focuses on mechanisms of reward processing, and their disruption in focal brain damage and Parkinson’s disease.

Sanjay Manohar – Motivation as a precision cost

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