Satisfying a need for sleep

Recent studies have suggested that the average individual has a sleep requirement in excess of 8h sleep each night. These concerns stem from reports of relatively increased propensity for sleep throughout the day for otherwise apparently healthy, young adults. It has been claimed that a substantial proportion of these individuals are suffering from a chronic loss of sleep. The work presented in this thesis focuses on two key issues: (i) the adequacy of current social norms of sleep behaviour, and (ii) the assumption that an increased propensity for sleep throughout the day is the single most reliable consequence of a failure to satisfy a physiological need for sleep. Throughout the first experiment the potential benefits of sleeping for as much as 10h per night were explored. During 26 consecutive nights EEG recordings and/or actigraphs were used to monitor the night-time sleep of 10 asymptornatic regular sleepers (mean 23.6y). The schedule comprised 7 nights of BASELINE sleep, 14 nights of EXTENDED sleep (up to 10h/night), and 5 nights of RECOVERY sleep. During EXTENDED sleep subjects slept significantly longer (approx. 1h) but sleep latency and interim wakefidness deteriorated. EXTENDED sleep produced no improvements to self-rated mood or subjective sleepiness. Vigilance tests showed a small but significant reduction in reaction time following EXTENDED sleep compared with both BASELINE and RECOVERY nights. Ability to detect target tones did not change significantly. An objective measure of daytime sleepiness - the Multiple Sleep Latency Test (MSLT) - showed small (approx I min) reductions during EXTENDED sleep. These findings give little support to the view of chronic sleep deprivation in the average 7.5 h sleeper. The second section includes evidence of a number of circumstances in which sleep can occur in alert subjects who otherwise showed no indication of sleepiness related impairment : (i) by using non-conventional scoring criteria throughout MSLT trials, sleep was found to occur as short bursts, or microsleeps, in non-arousing situations (ii) in response to a motivational incentive, and (iii) as MSLT defined patholo 91 sleepiness unrelated to sleep-sensitive performance tasks, subjective sleepiness, or prior sleep behaviour. It is concluded that the capacity for more sleep at night, and the ability to fall asleep quickly during the day, are not systematically related to a physiological need for sleep for many healthy, regular sleeping young adults.