Anne Urai wins the 2016 ABC poster award
Serial dependencies in decision-making, the biasing of choices by preceding choices and evidence, are a pervasive aspect of choice behaviour. We hypothesised that decision-makers' uncertainty about their preceding choice shapes serial choice biases by recruiting the arousal systems of the brainstem. These systems are in an ideal position to transform decision uncertainty into adjustments of behaviour: They receive descending projections from frontal brain regions encoding decision uncertainty and have widespread modulatory effects on their cortical target networks. We measured pupil diameter, a proxy for central arousal state, in human observers performing a perceptual choice task. Increases in pupil-linked arousal, after choice but before external feedback, scaled monotonically with decision uncertainty. This post-decisional arousal response promoted choice alternation, neutralising a predominant bias for choice repetition across the group of observers. We conclude that decision uncertainty drives rapid changes in central arousal state, shaping the serial correlation structure of choice behaviour.