Control and coding of pupil size by hypothalamic orexin neurons

Brain orexin (hypocretin) neurons are implicated in sleep-wake switching and reward-seeking, but their roles in rapid arousal dynamics and reward perception remain unclear. Here, cellspecific stimulation, deletion, and in vivo recordings revealed strong correlative and causal links between pupil dilation - a quantitative arousal marker - and orexin cell activity. Coding of arousal and reward was distributed across orexin cells, indicating that they specialize in rapid, multiplexed communication of momentary arousal and reward states.