The Peptide That Keeps You Awake

Orexin A is the most direct pharmacological handle on wakefulness. Produced in just a small cluster of hypothalamic neurons, it excites the brain's arousal systems — norepinephrine, serotonin, histamine, dopamine — to sustain the wake state and prevent inappropriate transitions into sleep.

The clearest demonstration of its importance is narcolepsy: patients who lose their orexin neurons develop the disorder, with uncontrollable sleep attacks and fragmented REM. That cause-and-effect — delete the peptide, lose wakefulness — is the strongest evidence in all of neuroscience that orexin is the master arousal switch. Members discuss it as a research window into how the brain decides to be awake at all.