The orexin system in the lateral hypothalamus and dorsal medical hypothalamus/perifornical area is activated during wakening and silent during sleep. It is the system that is disrupted in narcolepsy. It is also the system that coordinates the activity of the other arousal centers in the brain including the TMN-HA, LC-NE, DRN-5-HT, VTA-DA, and cholinergic neurons in the Nucleus Basalis of Meynert (NBM-Ach).