Inclusion Criteria:  Age 65-85. Self-report mean sleep efficiency (the time in bed spent asleep within the time of lights out to final awakening) < 90% based on diary and actigraphy estimates and wake time after sleep onset > 20 minutes based on diary and actigraphy estimates. Self-reported normal or corrected-to-normal visual and auditory acuity.  Exclusion Criteria:  Shift work involving night shift or regular work after 9pm. Presence of a chronic condition that significantly affects sleep. Severe psychiatric condition including major depressive disorder, panic disorder, substance use disorders, and alcohol abuse/dependence within the past 6 months, or a lifetime history of a psychotic disorder or bipolar disorder, based on initial online/phone self-report diagnoses, and subsequently based on the M.I.N.I International Neuropsychiatric Interview. Current use of medications affecting sleep such as antidepressants, antipsychotic medications, anticonvulsants, and steroids. Current use of sedating drugs used at bedtime. Consumption of > 14 alcohol drinks per week or > 6 drinks at a single sitting. Consumption of > 3 caffeine drinks per day. Prior diagnosis of a Central nervous system (CNS) disease, such as multiple sclerosis, stroke, Parkinson's disease, Alzheimer's disease, seizure disorder, delirium or dementia, a loss of consciousness > 24 hours, or traumatic brain injury as identified by the Cumulative Illness Rating Scale for Geriatrics (CIRS). Participants who are diagnosed with Alzheimer's disease based on neuropsychological testing will be excluded. Sleep efficiency > 90% and wake time after sleep onset < 20 minutes consistent with the rationale of the inclusion criteria described above. Apnea/hypopnea index greater than 15 as determined by one night of Apnea Link Plus screening. Metal in the body. Rationale: Due to the nature of magnetic resonance imaging (MRI), participants cannot have any metal implants in their bodies, cannot have worked in a metal shop or been exposed to metal fragments during combat. Metal dental work (e.g. fillings crowns) may be allowed if compatible with the MRI scanner. Claustrophobia. Rationale: Could prevent the participant from completing the MRI scans. Severe obesity. BMI > 40. Rationale: Could prevent the participant from completing the MRI scan. Near-miss or prior automobile accident "due to sleepiness" within the past 12 months. Rationale: reduces the risk of sleepiness-related accidents. Employed as a commercial driver during the study (for example, bus drivers, train engineers, airplane pilots). Rationale: reduces the risk of sleepiness-related accidents. A score below 23 on the Telephone Interview for Cognitive Status. Rationale: This cut-off has been demonstrated to differentiate well between individuals with mild cognitive impairment from individuals with dementia who would have decision making impairments (Seo et al. 2011, Archives of Gerontology and Geriatrics). This ensures that decision making abilities are intact.