Locus coeruleus neuromelanin predicts ease of attaining and maintaining neural states of arousal

The locus coeruleus (LC), a small subcortical structure in the brainstem, is the brain’s principal source of norepinephrine. It plays a primary role in regulating stress, the sleep-wake cycle, and attention, and its degradation is associated with aging and neurodegenerative diseases associated with cognitive deficits (e.g., Parkinson’s, Alzheimer’s). Yet precisely how norepinephrine drives brain networks to support healthy cognitive function remains poorly understood – partly because LC’s small size makes it difficult to study noninvasively in humans. Here, we characterized LC’s influence on brain dynamics using a hidden Markov model fitted to functional neuroimaging data from healthy young adults across four attention-related brain networks and LC. We modulated LC activity using a behavioral paradigm, and also measured individual differences in LC neuromelanin. The model revealed five hidden states, including a stable ‘arousal’ state that occurred when subjects actively engaged with the task. LC neuromelanin correlated with this state’s stability across experimental manipulations, and with subjects’ propensity to enter into and remain in this state. These results provide new insight into LC’s role in driving spatiotemporal neural patterns associated with attention and arousal, and demonstrate that neuromelanin variation can explain individual differences in these patterns even in healthy young adults. ### Competing Interest Statement The authors have declared no competing interest.