The neurobiology of decision making under risk

Risk is a highly salient psychological decision variable, and sensitivity to risk is an evolutionarily \nancient attribute. In this thesis I address the neurobiological foundation of risk assessment, and \nshow that behaviour is driven by an underlying distributed neural representation of different \nelements of risk in the brain. In particular, I show using fMRI (in Chapter 4) and MEG (in Chapter \n8) that variance (dispersion) and skewness (asymmetry) of gambles evokes anatomically \nseparable neural responses in a parietal, prefrontal and insula cortical network. I discuss \npossible theoretical neurobiological mechanisms by which preferences could be imbued to \nchoice, and show that subjective tastes for risk, in terms of behavioural sensitivity to each of \nthese risk dimensions, influences the encoding of risk and subsequent anticipatory responses. \nIn Chapter 5, I show that a representation of prospective outcomes several trials into the future \nis supported by a dissociated encoding of the statistical information of future states in medial \nprefrontal cortex; furthermore that this encoding is contingent upon overarching goals or \nconstraints. \nIn Chapter 6, I demonstrate that economic choice is highly susceptible to exogenous biological \ninfluences, namely the effect of metabolic state, whilst in Chapter 7 I provide evidence that the \nencoding of risk is not affected by dopaminergic disruption, suggesting that dopamine might \nmediate effects on risk-taking via its role in reward feedback representation. \nIn summary, the studies in this thesis elaborate the neural mechanisms underlying how humans \nmake both single-shot and sequential decisions under risk, central elements in decision-making \nscenarios ranging from foraging to financial investment. This demonstrates that phylogenetically \nancient circuitry subserving valuation and reward decompose choice into their salient statistical \nfeatures, enabling the sophisticated representation of the future and its alternatives.