The influence of contextual reward statistics on risk preference

Decision theories mandate that organisms should adjust their behaviour in the light of the contextual reward statistics. We tested this notion using a gambling choice task involving distinct contexts with different reward distributions. The best fitting model of subjects' behaviour indicated that the subjective values of options depended on several factors, including a baseline gambling propensity, a gambling preference dependent on reward amount, and a contextual reward adaptation factor. Combining this behavioural model with simultaneous functional magnetic resonance imaging we probed neural responses in three key regions linked to reward and value, namely ventral tegmental area/substantia nigra (VTA/SN), ventromedial prefrontal cortex (vmPFC) and ventral striatum (VST). We show that activity in the VTA/SN reflected contextual reward statistics to the extent that context affected behaviour, activity in the vmPFC represented a value difference between chosen and unchosen options while VST responses reflected a non-linear mapping between the actual objective rewards and their subjective value. The findings highlight a multifaceted basis for choice behaviour with distinct mappings between components of this behaviour and value sensitive brain regions. •We use fMRI and a novel gambling paradigm to study the influence of the contextual reward statistics on decision making under risk•Risk propensity is influenced by the distribution of rewards available in a given temporal context, an effect that relates to activity in ventral tegmental area/substantial nigra•ventral striatum encodes elements of subjective, rather than objective, value during decision making under risk•activity in ventromedial prefrontal cortex reflects the subjective value difference between chosen and unchosen option and not the average value across options