Twenty-Three Years of Hypocretins: The "Rosetta Stone" of Sleep/Arousal Circuits.

The discovery of the hypocretins/orexins (HCRTs) has revolutionized sleep science in the last two decades. A combination of anatomical tracing methods, optogenetics, and pharmacology is delineating a blueprint of functional inputs and outputs of the HCRT system. Here, we discuss several models of HCRT action that involve the integration between physiological variables, circadian output, and sleep homeostasis. Generation of activity maps during the sleep-wake cycle at the cellular level will allow investigators to decipher computational frameworks modeling operations of HCRT networks.