The Locus Coeruleus: Where Cognitive and Emotional Processing Meet the Eye

The pupil offers a window into how arousal shapes the way we think, learn, and behave. Yet, arousal is a complex and multifaceted construct, leaving many open questions about the relationship between pupil size and different neurocognitive processes. Exciting new research has linked pupil measures to activity in the locus coeruleus (LC), the brain’s primary supplier of norepinephrine (NE), creating new opportunities to study a neuromodulatory system that long seemed inaccessible in human research. In this chapter, we review evidence showing that pupillometry reveals the role of the locus coeruleus-norepinephrine (LC-NE) system in energizing attention and amplifying mental selectivity. We also synthesize computational and neurobiological models of how the LC-NE system implements neural gain, a process by which salient information is enhanced and lower priority information is suppressed. In the latter half of the chapter, we turn to a classic dual-curve model of arousal-performance interactions to explain what (quality of information processing), when (level of arousal), and where (locus of priority signal) LC activity influences information processing in the brain. We conclude by summarizing how pupillometry can be used to test the influence of LC activation on the key parameters of attention and arousal.