Inclusion Criteria:  Age 25-50 years. Primary language is English. Normal cognition. Normal (or corrected-to-normal) vision and hearing. Current depression.  Stable, normally-timed sleep-wake cycle as determined by interview, 1-week daily sleep log, and 1-week wrist actigraphic evidence, and defined by:  Habitual nocturnal sleep duration between 6h and 9h. Habitual bedtime between 9pm-12am. No evidence of habitual napping.  Exclusion Criteria:  Current or prior medical condition that could interfere with collection or interpretation of data, based on medical history. History of stroke, epilepsy, brain scarring, or head injury causing unconsciousness. Independent/Intrinsic sleep disorder other than insomnia based on history or polysomnogram. Recent use of psychoactive medications or medication thought to impact sleep or CNS function, as determined by investigators (e.g. SSRIs, benzodiazepines, glutamate modulators, gabapentin). History of or current psychiatric conditions that increase study risk or grossly impair CNS function (e.g., current anorexia or bulimia, history of substance dependence or current substance abuse, lifetime history of psychosis). Lifetime history of electroconvulsive therapy. Pregnancy as determined by self-report. Travel beyond 2 time zones in the 2 months before study. Unwillingness to refrain from using alcohol or caffeine during the study.