At a fundamental level, sleep is exemplified by decreased consciousness, decreased responses to external stimuli, and decreased overall motor activity compared to wakefulness. Several brain neuroanatomical structures, genes, and neurotransmitter pathways play a role in sleep; however, no specific neurobiological mechanism(s) have been identified that specifically control the onset, maintenance, or termination of sleep. Electroencephalography (EEG), combined with electrooculography (EOG) and electromyography (EMG), are the basis upon which the two major types of sleep (i.e., rapid eye movement 【REM】 versus non-REM sleep), sleep staging (non-REM Stages 1-3), and architecture are defined.