• Changes in sleep and waking EEG measures [ Time Frame: During 3-week chronic sleep restriction segment of inpatient study ] [ Designated as safety issue: No ]
  
• frequent measures of performance, attention, alertness, and memory [ Time Frame: During 3-week chronic sleep restriction segment of inpatient study ] [ Designated as safety issue: No ]
  
• measures of cardiovascular and metabolic function [ Time Frame: During 3-week chronic sleep restriction segment of inpatient study ] [ Designated as safety issue: No ]
  

Behavioral: chronic sleep restriction
5.6 hours of sleep per 24 hours for 3 weeks

It has long been recognized that sleep patterns change with age. A common feature of aging is the advance of the timing of sleep to earlier hours, often earlier than desired. Polysomnographically-recorded sleep in older people shows an increased number of awakenings, a reduction of stages 3 and 4 (SWS) sleep, and a flattening of REM sleep distribution throughout the night. These age-related changes are found in even healthy individuals who are not taking medications and who are free from sleep disorders. In addition to these sleep disturbances, many older individuals curtail their sleep voluntarily, reporting similar rates of sleep restriction (sleeping less than 7 or less than 6 hours per night) as young adults. Whether voluntary or not, insufficient sleep has medical, safety and metabolic consequences. In fact, converging evidence in young adults suggests that sleep restriction per se may impair metabolism, and that reduced sleep duration is associated with weight gain, obesity, diabetes, cardiovascular disease, and mortality.

The study begins with 21 days of outpatient study in which the participants will be required to sleep for 10 hours each night in order to ensure they are well-rested. This will be followed by a 39-day inpatient study. The study will begin with 3 "sleep satiation" days during which all participants will be scheduled to sleep for 12 hours per night and have a 4 hour nap each afternoon. This is followed by 3 baseline days in which the participants will follow the same sleep-wake schedule they were following at home. Following this, the participant will undergo 3 weeks of chronic sleep restriction while living on a non-24-hour schedule. The participant will live on a schedule that is equivalent to 5.6 hours of sleep per 24 hours. Following these 3 weeks, the participant will be scheduled to again sleep for 10 hours per night for 10 nights.