Sleep is the biological process that a person spends almost a third of their life doing. After decades of research, we still cannot say we have a full understanding of this process. One thing that is safe to say is that it has a function; considering the large amount of time that organisms spend on it, if it was not adaptive, it would not survive through evolution. As for what kind of function it serves, there is still no definite answer (Pinel 1999 [Rechtschaffan 1998]). But there are two main theories that are trying to explain what we do know so far.

The first theory is the Recuperation Theory, which is the way most people perceive and explain sleep. It sees sleep as a repairing process that reverses the imbalance of our system caused by daily activity. It assumes that activities during our wakefulness disturbs our body's homeostasis. The common concept of needing more sleep to 'catch up' previously lost sleep would belong to this theory.

The second theory is the Circadian Theory. It explains that sleep is just a way for animals

As mentioned before, sleep deprivation can lead to a variety of personal and motivation problems, and memory deficits of certain material. Other effects of sleep deprivation are impairment of innovative thinking and flexible decision making (Binks, Waters & Hurry 1999), poor performance on vigilance tasks (Pinel 1999 [Gillberg et al. 1996]) and increase of sleepiness and microsleeps. Even though sleep-deprived people often report feeling tired and emotionally disturbed, and they do perform poorly on passive cognitive tasks, but many of the negative effects of sleep deprivation are confounded by other factors such as stress and circadian disruptions (Pinel 1999). Since these other factors could well contribute to negative effects, and in fact they were the cause the people loss sleep in the first place, we cannot consider these personal experiences as effects of sleep deprivation alone.

There are two studies that looked at long term sleep reduction. The first one is Webb & Agnew's (1974) in which a group of 16 participants reduced their sleep to 5.5 hours per night for 60 days. Only one deficit was reported, on an extensive battery of mood, medical and performance test, which was a slight deficit of auditory vigilance (Pinel 1999).

Another reason why negative effects of sleep deprivation are exaggerated is due to the effect of microsleeps. A person's cognitive abilities for demanding tasks like abstract reasoning and spatial relations are not effected even after one night of sleep deprivation (Percival, Horne & Tilley 1983), but in fact when faced with less demanding tasks like driving, a person would easily drift into microsleeps, thus leading to serious problems. It has also been reported that even for sleep deprivation up to 72 hours, there was no effect on strength or motor performance, except for reducing the time to exhaustion (Van Helder & R

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