Brainstem fMRI signaling of surprise across different types of deviant stimuli

The detection of deviant stimuli is crucial to orient and adapt our behavior. Previous work showed that infrequent (hence deviant) stimuli elicit phasic activation of the brainstem locus coeruleus (LC), which releases noradrenaline and controls central arousal. However, it is unclear whether the detection of behaviorally-relevant deviant events selectively trigger LC responses, or also other neuromodulatory systems related to dopamine, acetylcholine, and serotonin. Here, we combined human fMRI recordings optimized for brainstem imaging with pupillometry (a peripheral marker of central arousal) to perform a mapping of deviant-related responses in subcortical structures. Participants had to detect deviant items in a "local-global" paradigm that distinguishes between deviance based on the stimulus probability and the sequence structure. fMRI responses to deviant stimuli were quite distributed, detected in the LC but also other subcortical nuclei and many cortical areas. Both types of deviance elicited responses in the pupil, LC and other neuromodulatory systems. Our results reveal that the detection of task-relevant deviant items recruits the same multiple subcortical systems across computationally different types of deviance.