Brown University scientists find pupil dilation signals rapid brain adaptation to surprise

Brown University neuroscientists found that pupil dilation during surprise signals rapid brain adaptation, enabling faster learning from unexpected information. This discovery was published in Nature Human Behaviour. In experiments with colored squares, 63 participants saw unexpected colors, producing pupil expansion and specific EEG waves tied to norepinephrine from the locus coeruleus, which updates mental context. These markers correlated with reduced bias and quicker adjustments. The response reflects “fight-or-flight” noradrenaline bursts that replace outdated mental context with a “clean slate,” reducing previous bias and accelerating learning in changing environments.