Why do us need snooze

"Your mind is processing complex thoughts, making memories stick, clearing out brain waste and much more." BY SARAH DIGIULIO

From the outside, most people don't look very active during sleep. But what's going on inside is an entirely different story- particularly for our brains.

"It's not just that the brain turns off," explains Carl Bazil, M.D., Ph.D., director of epilepsy and sleep division of the department of neurology at New York- Presbyterian/ Columbia University Irving Medical Center,

In healthy sleep , the brain is cycling through four sleep stages, each distinguished by a unique pattern of brain activity ( learn more about the stages of sleep ), he explains. Neuroscientists and sleep-medicine doctors can measure this brain activity during sleep using a test called an electroencephalogram, or EEG ( a series of electrodes is attached to the scalp to detect and record electrical signals in the brain. According to Dr. Bazil, "Sleep is actually a very active process."

One theory as to why human brains need sleep in the first place is to retain their neuroplasticity- the ability for our brain cells to strengthen important connections and get rid of the less important ones ( the "synaptic homeostasis hypothesis," which is still a very active area of research), explains Spencer Dawson, Ph.D., a postdoctoral fellow in neurology at Northwestern University Feinberg School of Medicine.

During the day, when we're awake and exposed to new information ( whether it's in a classroom, at a party talking to a friend, while playing a sport or just observing the world around us), our brain cells are brewing these new connections, Dawson says.

We require an incredible amount of energy to maintain those new connections - and, at some point, the brain need to downscale these connections, he says. "Sleep seems to be critical for this."

Studies show that if sleep doesn't happen, things, like storing memories, learning new information, honing our deep learning and analytical skills, cleaning out brain "waste" and being able to control our moods and emotions either, doesn't happen or doesn't happen very well. Here's some of what's happening in your brain during sleep.

The brain is encoding memories

Sleep is critical for learning new information, which is something neuroscientists call "memory consolidation", according to Dr.Bazil. Research shows that if you teach something to a group of people in the evening and test them on it the next morning, those who get a good night's sleep do much better at recalling the information than people whose sleep is restricted.

More interesting, research suggests that if you teach something to a group of people in the evening and test them on it 12 hours later , in the morning , after a good night's sleep , they do better than people who learning something in the morning and are tested 12 hours later, in the evening, who have not slept during the day.

It's during the deep stages of sleep when memories appear to get translated from the hippocampus( the part of the brain that holds on to new memories for short-term storage) to the prefrontal cortex. ( where long-term memories are stored), Dawson notes.

"It's clear that you need sleep to learn," Dr.Bazil says. Read: This is why staying up all night to cram for a test doesn't work.

You learn new skills

The brain needs sleep to process new things so it would make sense that the brain also needs sleep to learn new motor skills. That is why if you're learning an action or set of actions (like how to play a musical instrument or a new dance routine), you're more likely to be better at that task after a good night's sleep.

Your brain figures out how to apply new information in different Scenarios

Have you ever been faced with a tough problem or decision and been told to "sleep on it"? There's a scientific explanation for why that works, Dr. Bazil says. "Sleep is when you do complex processing and come to conclusions about complex information."

These types of complex processing skills are essential when it comes to things like learning a new language, coming up with new theories and being able to apply certain principles to new problems.

Your ability to focus is improved

If you've ever stayed up into the wee hours of the morning in order to meet a work deadline or finish a paper, you can probably relate to it being harder to concentrate the more hours you're awake. Indeed, research reveals that if you completely deprive someone of sleep for 36 hours, they will perform poorly on simple attention tasks.

Research also shows that if a healthy individual gets only six hours of sleep per night, performance on attention tests deteriorates over time. By about day eight or 10, concentration is about the same as that of someone who is completely sleep deprived.

"People don't realize they're sleep deprived, but they're just not reacting as quickly," says Dr.Bazil.

Sleep helps maintain executive functioning skills

The frontal cortex is particularly vulnerable to sleep loss, and that part of the brain is critical for executive functioning (which includes decision making and judgment).

Studies show that the longer someone is awake, risk tolerance heightens, Dawson says. "You are going to be more likely to make risky decisions toward the end of the day and into the night - more so than you would during the day."

It makes you less moody, less irritable and less likely to lash out 

Do you think the sleep loss can make you cranky? That effect is thought by neuroscientists to be a result of having your amygdala- the emotional center of the brain - go into overdrive.

In a healthy, well-rested person, the amygdala and the prefrontal cortex work together to keep your emotional state in check. Something happens in our environment ( for example, someone cuts us off on the road or tells us good news), and the amygdala is the part of the brain where our reaction comes from. The prefrontal cortex is on standby to help reign in that response if things get a little too heated.(Think of it as the emotional "brakes," Dawson explains.)

When we're sleep deprived, however activity in the amygdala revs up, while activity in the prefrontal cortex slows down. "It's essentially as if someone cut the brake lines," Dawson says. " So we tend to be more moody , irritable, quick to anger and reactive - and we have a harder time controlling our behavior." 

The brain gets rid of its "waste"

While the brain sleeps, the harmful toxin is cleared out . Although the research behind the brain's purge of neurotoxic waste is still in its infancy, it's exciting , because there are a lot of implications for downstream effects , notes Dawson.

There are certain proteins that seem to accumulate in the brain over the course of the day when someone awake- and those proteins then get cleared out during sleep, Dawson explains. 

One is beta-amyloid, a sticky protein that can form larger clumps of plaque in the brain if enough of it accumulates. These plaques disrupt communication between brain cells and eventually kill them. The presence of these plaques in the brain is also one of the telltale signs of Alzheimer's disease.

Meanwhile, a recent meta-analysis of multiple studies that have examined the link between poor sleep and Alzheimer's disease risk shows that sleep problems do, in fact, pose a measurable risk for the chronic cognitive -impairment disorder.)