The maintenance of sustained alertness, or vigilance, is essential to cognitive processing of incoming information. We’re all familiar with the fact that lapses of vigilance are more likely to occur after sleep deprivation. These lapses prevent adequate cognitive information processing, with possibly disastrous effects, as in accidents. We investigate the brain processes associated with vigilance. Can we obtain physiological measures that predict sleepiness? Can vigilance be manipulated at the systems level rather than pharmacologically? What are the brain mechanisms involved in lapses of vigilance and their aggravation? We address these questions in young and elderly people, in narcolepsy and insomnia. Research tools include skin temperature assessment of autonomic nervous system correlates as well as fMRI, High Density EEG and eyelid, eye and pupil size tracking assessment of central nervous system correlates.