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.

對(duì)大多數(shù)人來(lái)說(shuō)，睡眠是咖啡的近親；睡眠是寶貴的天賦，是早在人類進(jìn)化初期就賦予了我們的天賦。但我們究竟為什么需要睡眠？睡眠又究竟是由哪些部分組成的呢？?jī)H僅是這樣的問(wèn)題，長(zhǎng)期以來(lái)卻仍然困擾著科學(xué)家們。一項(xiàng)新的研究試圖解釋我們?yōu)槭裁此�覺(jué)。

這項(xiàng)研究的作者，Chiara Cirelli 和 Giulio Tononi將對(duì)睡眠的探究形容為探究神化中的鳳凰，同時(shí)他們認(rèn)為雖然我們還不了解睡眠的目的究竟是什么，但是從所有的動(dòng)物都睡覺(jué)這一點(diǎn)可以看出睡眠一定是非常重要的。

有科學(xué)家認(rèn)為，對(duì)哺乳動(dòng)物與鳥類而言，睡眠本身并不重要，它僅僅是一種強(qiáng)制動(dòng)物進(jìn)入靜止?fàn)顟B(tài)的方式。Cirelli 和 Tonon不同意這種觀點(diǎn)，他們指出，目前為止還沒(méi)有任何證據(jù)表明有什么動(dòng)物是不睡覺(jué)的。

即使是海豚這樣，由于一刻不停地游動(dòng)而常常被認(rèn)為不睡覺(jué)的動(dòng)物，其實(shí)也早已發(fā)展出了其特殊的睡覺(jué)方式。在游泳時(shí)，海豚會(huì)睜一只眼閉一只眼，它們關(guān)閉一側(cè)的腦部，其腦電波表現(xiàn)出了深度睡眠時(shí)的慢波特征。

Cirelli說(shuō)，海豚發(fā)展出了如此不同尋常的特化作用而不是簡(jiǎn)單地?cái)[脫睡眠，這一重要事實(shí)正可以被看作是證明睡眠具有不可缺少的重要功能的證據(jù)。

Cirelli同時(shí)將睡眠剝奪及長(zhǎng)時(shí)間不睡覺(jué)的后效作為證明睡眠必要性的例子。已有研究表明，睡眠剝奪會(huì)導(dǎo)致諸如老鼠、蒼蠅和蟑螂等動(dòng)物的死亡，也會(huì)引起基因性失眠癥患者的死亡。而一個(gè)缺乏睡眠的人會(huì)睡很長(zhǎng)時(shí)間，以此來(lái)恢復(fù)精神。

他們的假設(shè)認(rèn)為，睡眠是大腦在一天的辛苦工作之后，進(jìn)行重組的一種方式。睡眠可以使高速緊張的神經(jīng)突觸得以減速，并回復(fù)到基線水平。腦部要用其80%的能量來(lái)維持神經(jīng)沖動(dòng)的發(fā)生，顯然腦部是需要休息的。

同時(shí)他們指出，睡眠為鞏固一天中新的記憶，并且拋棄掉一些比較舊的、隨機(jī)的、不太重要的記憶提供了可能。從理論上看，這將使新的一天里得以獲得更多的知識(shí)。Cirelli總結(jié)道：“盡管在動(dòng)物為什么需要睡覺(jué)這個(gè)問(wèn)題上，還沒(méi)有統(tǒng)一的共識(shí)，但是對(duì)睡眠的核心功能的探究，尤其是在其細(xì)胞水平上的探索，仍然是一項(xiàng)很有價(jià)值的實(shí)踐。”