Abstract
Fear can be induced either through direct experience of threat or through observation of others’ distress. This capacity for observational fear provides a survival advantage by enabling vicarious, social learning of potential danger and forms a foundation for empathy. While the anterior cingulate cortex (ACC) has long been implicated in mediating observational fear, the neuromodulatory mechanisms that distinguish it from direct fear have been unclear. Our recent work demonstrates that the locus coeruleus (LC), the brain’s major noradrenergic nucleus, contributes in a lateralized manner to these distinct states. Specifically, the right LC→ACC pathway is required for sustaining vicarious freezing, but not for direct fear. This finding shifts the view of the LC from a diffuse arousal center to a differentiated neuromodulatory hub that separates self-referenced and socially acquired fear. Extending the principle of hemispheric specialization into neuromodulatory systems, the LC lateralization illustrates how ancient brainstem nuclei have been adapted to support the demands of social survival. This insight highlights a broader principle: neuromodulatory nuclei act as specialized contributors to distinct fear states.
Keywords
Vicarious fear, Locus coeruleus, Anterior cingulate cortex, Hemispheric lateralization, Empathy, Noradrenergic system