Fig. 1. Sagittal schematic drawing of the human brain illustrating regions that contribute to the regulation of sleep and wakefulness. The diagram emphasizes regulation of physiologic traits and arousal states by neural circuits that are distributed throughout the brain. EEG = electroencephalographic; REM = rapid eye movement; NREM = non–rapid eye movement. From Hobson and Pace-Schott;  used with permission from  Nature (  http://www.nature.com/).