Neuroscientists have a new explanation for why we sleep

Whether we like it or not, we all need to sleep, but despite years of research, the reason why has remained just beyond our grasp. However, now, two neuroscientists have a new explanation for it, and their answer presents a very different idea than we've seen before.

We've probably all forced ourselves to stay awake longer than we should at some point in our lives. We needed to study for an important test or get caught up on a backlog of work, or we needed to see the opening-night midnight showing of an awesome new movie. The consequences of that are pretty well known too: it gets harder to think clearly, our concentration wavers and we make poor decisions. It's easy to think that this is because our brain is running out of energy, but that's apparently not the case.

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Scientists have known for awhile that the brain is just as active during sleep as it is while we're awake. It's long been thought that the reason for this may be that the brain is working to strengthen all the neural connections we've made during the day. However, a new idea put forward by Giulio Tononi and Chiara Cirelli, neuroscientsts at the University of Wisconsin, says it may be the exact opposite.

This new hypothesis essentially says that the brain can only handle so much of this strengthening of neural connections, and we experience the mental fatigue as our brain simply can't take any more. Sleep, they say, may actually weaken these mental connections, bringing the brain's cells back down to a 'base state' from which we can start fresh when we wake up.

"More than 20 years ago, when we worked together at the Sant'Anna School of Advanced Studies in Pisa, Italy, we began to suspect that the brain's activity during slumber may somehow restore to a baseline state the billions of neural connections that get modified every day by the events of waking life," they wrote in a Scientific American article. "Sleep, in this telling, would preserve the ability of the brain's circuitry to form new memories continually over the course of an individual's lifetime without becoming oversaturated or obliterating older memories."

They call this new idea SHY — synaptic homeostasis hypothesis.

SHY may seem counter-intuitive. How can we retain memories of all the important things in our day if our brain is being reset down to this base state every night? The importance of things may be the key to that, though. As the brain works during the night, it's apparently processing everything we did during the day, maintaining the connections that were important — such as the ones involved in getting the correct answer to a problem, or the ones that mesh better with important memories from the past — and weakening the rest. The researchers call this 'down selection'.

"Down selection would ensure that insignificant events would leave no lasting trace in our neural circuitry, whereas memories of note would be preserved," Tononi and Cirelli wrote. "As an additional bonus, down selection would also make room for another cycle of synaptic strengthening during wakefulness."

Tononi and Cirelli's research doesn't answer all the questions about sleep and it's still not the final answer, but it brings us closer to understanding this important part of our lives.

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Personally, I'm someone who could certainly use more sleep, but at the same time, I always lament that 'lost' time, since there's so much I want to accomplish in the day. I know it's necessary to sleep, but that nagging question of 'why' has always been there. With science getting closer to figuring that out, maybe I can rest a little easier... or sign up for the treatments when they figure out how to let us 'down select' while staying awake!

(Photo courtesy: Getty Images)

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