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Title: Learning and action in uncertain environments
Author: Marshall, L.
ISNI:       0000 0004 7225 232X
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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Successful interaction with the environment requires flexible updating of our beliefs about the world. By learning to estimate the likelihood of future events, it is possible to prepare appropriate actions in advance and execute fast, accurate motor responses. According to theoretical proposals, humans track the variability arising from dynamic environments by computing various forms of uncertainty. Several neuromodulators have been linked to uncertainty signalling but comprehensive empirical characterisation of their roles in perceptual belief updating and motor response modulation has been lacking. This thesis interrogates the contributions of noradrenaline, acetylcholine and dopamine to human learning and action within a unified computational framework of uncertainty. First, I use pharmacological interventions to characterise the impact of noradrenergic, cholinergic and dopaminergic receptor antagonism on individual computations of uncertainty during a probabilistic serial reaction time task. I develop and employ a hierarchical Bayesian model to quantify human learning and action under three forms of uncertainty. I propose that noradrenaline influences learning of uncertain events arising from unexpected changes in the environment, while acetylcholine balances attribution of uncertainty to chance fluctuations within environmental contexts or to gross environmental violations following a contextual switch. In contrast, dopamine supports the use of uncertainty representations to engender fast, adaptive responses. Second, I extend these results by focusing on the effects of natural inter-individual variations in dopaminergic function. Specifically, I employ the same task and model to assess individual learning and action under uncertainty as a function of COMT genotype. Third, I focus on the role of noradrenaline. Uncertainty computations have been linked to changes in pupil diameter, and pupil dilation to noradrenergic neuronal activity in the locus coeruleus. Combining an auditory probabilistic learning task, pharmacological manipulations, pupillometry and computational modelling, I demonstrate that pupil diameter offers an indirect measure of dynamic noradrenergic computations of environmental uncertainty and volatility.
Supervisor: Bestmann, S. ; Kennerley, S. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available