Effects of Sleep Deprivation and Recovery on Cognitive Functions

This study will measure brain activity in individuals performing language tasks while in various states of alertness to learn more about how the central nervous system is affected by impairments such as sleepiness. Healthy normal volunteers between 20 and 40 years of age may be eligible for this study. Candidates must be non-smokers, right-handed, speak English fluently and have at least 12 years of education. They are screened with a medical history, physical examination, hearing and speech evaluation, computer task training, blood and urine tests and a late-night functional magnetic resonance imaging (fMRI) scan (see description below). Before screening and again before participating in the study, candidates wear an actigraph (a wristwatch-like device that records motion) for 7 days to provide a measure of their sleep-wake patterns. Participants undergo the following tests and procedures: * Extended wakefulness: Subjects are kept awake longer than is normal for them in their everyday life to be able to examine the brain under conditions of sleepiness. They are engaged in activities with the research staff during this waking time. * Functional magnetic resonance imaging: Subjects undergo five separate fMRI scans-one during screening and four others during the main part of the study. fMRI uses a magnetic field and radio waves to produce images of the brain. The subject lies on a table that is moved into the scanner (a narrow cylinder), wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. Brain scans are taken at rest and while the subject performs tasks, which include pressing a button upon seeing certain shapes and performing various language tasks, such as saying memorized or new words, listening to narratives, and describing everyday procedures. * Neurological, speech-language, and neuropsychological testing: Before the fMRI exams and during the period of extended wakefulness, subjects complete a series of tests