Extensive electroencephalographic (EEG) sleep studies have demonstrated increases in rapid eye movement (REM) sleep and changes in non-rapid eye movement (NREM) sleep in depression. Preclinical evidence shows that REM sleep is generated in the brainstem. It also shows that NREM sleep is characterized by slower frequency, higher amplitude thalamocortical electrical oscillations. The alterations in NREM sleep in depressed patients may lead to impaired restoration of prefrontal cortex function during NREM sleep. Functional neuroimaging studies of sleep extend the preclinical understanding of the mechanisms of sleep/wake regulation by providing potential links between neural systems involved in emotional behavior and those involved in sleep. The notion of hyperarousal in paralimbic structures in depressed patients has received further support from an extensive literature describing the functional neuroanatomical correlates of the antidepressant response to sleep deprivation in depressed patients. Patients with schizophrenia are known to have severely disturbed subjective sleep.