A Conserved Locus Coeruleus fMRI Signature of Brain-State Transitions across Sleep, Anesthesia, and Wakefulness

Neuromodulatory systems dynamically reconfigure large-scale brain networks to support adaptation across behavioral and cognitive states. The locus coeruleus (LC), which broadcasts noradrenaline throughout the forebrain, is a central regulator of arousal and state-dependent dynamics. However, how LC activity manifests in brain-wide organization across physiological contexts, and how it biases fMRI connectivity, remains poorly understood. Using an optogenetically informed cross-species framework, we identify a transient LC-derived spatiotemporal pattern of brain activity accompanying brain-state transitions under progressively naturalistic conditions: controlled LC stimulation and endogenous LC fluctuations in anesthetized mice, sleep-wake transitions in rodents and humans, and resting-state activity in awake humans. This LC-derived signature is conserved across species and contexts, leaving a robust and detectable imprint on the BOLD signal. Critically, the prevalence of LC events systematically biases functional connectivity metrics in human fMRI. These findings establish LC activity as a mechanistically interpretable source of variability in resting-state measurements, with direct implications for the interpretation of fMRI biomarkers in arousal-related disorders.