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.