For many of us, sleep is a precious gift, akin to Coffee, that was gifted to us early on in our evolution. But scientists have long been completely baffled as to just why we sleep, and just what constitutes sleep anyway. A new study attempts to address just why we sleep.

"We don't understand the purpose of sleep, but it must be important because all animals do it," Chiara Cirelli and Giulio Tononi, the study authors say, who describes the search for sleep as like the search for the mythological phoenix.

Some scientists believe that sleep is not important by itself in mammals and birds, and is just a way to impose a quiet and immobile state. Cirelli and Tononi reject this opinion, pointing to the fact that, so far, there has been no evidence of any animal not sleeping.

Even the dolphin, which is often used as an example of an animal that does not sleep because it keeps moving, has developed its own method of sleeping. The dolphin shuts down one half of its brain, swimming with one eye closed, and exhibiting the slow waves characteristic of deep sleep.

"The very fact that dolphins have developed the remarkable specialization . . ., rather than merely getting rid of sleep altogether, should count as evidence that sleep must serve some essential function and cannot be eliminated," Cirelli says.

Cirelli also points to sleep deprivation, and the after-effect of having gone a long time without sleep, as examples of the necessity of it. Sleep deprivation has been shown to kill animals like rats, flies and cockroaches, as well as humans who suffer from genetic insomnia. And when a human rebounds from lack of sleep, they sleep for a long time to recuperate.

Their hypothesis suggests that sleep acts as a way for the brain to regroup after a hard day. Sleep theoretically gives the synapses – which have been escalating in strength during the day – a chance to slow down again, and return to a base level. Given that the brain uses 80% of its energy in order to keep the synaptic activity happening, there is an obvious need for the brain to rest.

They also suggest that sleep allows for the consolidation of new memories, and the trashing of older, random and unimportant memories from the day passed. This theoretically allows for more learning the following day. "While there may still be no consensus on why animals need to sleep, it would seem that searching for a core function of sleep, particularly at the cellular level, is still a worthwhile exercise," Cirelli concludes.

对大多数人来说，睡眠是咖啡的近亲；睡眠是宝贵的天赋，是早在人类进化初期就赋予了我们的天赋。但我们究竟为什么需要睡眠？睡眠又究竟是由哪些部分组成的呢？仅仅是这样的问题，长期以来却仍然困扰着科学家们。一项新的研究试图解释我们为什么睡觉。

这项研究的作者，Chiara Cirelli 和 Giulio Tononi将对睡眠的探究形容为探究神化中的凤凰，同时他们认为虽然我们还不了解睡眠的目的究竟是什么，但是从所有的动物都睡觉这一点可以看出睡眠一定是非常重要的。

有科学家认为，对哺乳动物与鸟类而言，睡眠本身并不重要，它仅仅是一种强制动物进入静止状态的方式。Cirelli 和 Tonon不同意这种观点，他们指出，目前为止还没有任何证据表明有什么动物是不睡觉的。

即使是海豚这样，由于一刻不停地游动而常常被认为不睡觉的动物，其实也早已发展出了其特殊的睡觉方式。在游泳时，海豚会睁一只眼闭一只眼，它们关闭一侧的脑部，其脑电波表现出了深度睡眠时的慢波特征。

Cirelli说，海豚发展出了如此不同寻常的特化作用而不是简单地摆脱睡眠，这一重要事实正可以被看作是证明睡眠具有不可缺少的重要功能的证据。

Cirelli同时将睡眠剥夺及长时间不睡觉的后效作为证明睡眠必要性的例子。已有研究表明，睡眠剥夺会导致诸如老鼠、苍蝇和蟑螂等动物的死亡，也会引起基因性失眠症患者的死亡。而一个缺乏睡眠的人会睡很长时间，以此来恢复精神。

他们的假设认为，睡眠是大脑在一天的辛苦工作之后，进行重组的一种方式。睡眠可以使高速紧张的神经突触得以减速，并回复到基线水平。脑部要用其80%的能量来维持神经冲动的发生，显然脑部是需要休息的。

同时他们指出，睡眠为巩固一天中新的记忆，并且抛弃掉一些比较旧的、随机的、不太重要的记忆提供了可能。从理论上看，这将使新的一天里得以获得更多的知识。Cirelli总结道：“尽管在动物为什么需要睡觉这个问题上，还没有统一的共识，但是对睡眠的核心功能的探究，尤其是在其细胞水平上的探索，仍然是一项很有价值的实践。”