Arousal increases locus coeruleus blood flow, salience-related brain responses, and modulates negative-valence attentional biases

The amygdala helps prioritize emotional over neutral information but responds similarly to positive and negative stimuli, making it unlikely to drive valence-specific effects within affective networks. We hypothesized that the locus coeruleus (LC) is a key contributor to negative biases in attention. Using ultra-high field 7T MRI in humans, we tested how arousal modulates emotional face processing in an oddball task. Arousal induced by isometric handgrip increased LC cerebral blood flow and amplified brain responses to target and angry faces, but not to happy faces. The amygdala exhibited valence-general responses unaffected by arousal. LC connectivity with the default mode network decreased during processing target and angry faces, and arousal further modulated responses in the salience network and visual cortex. Behaviorally, arousal enhanced recognition of angry faces and performance was linked to left LC activation. These findings highlight the LC as a key structure through which arousal shapes valence processing, biases attention, and informs mechanisms related to affective disorders.