To sleep, perchance to forget

February 17, 2018 by Susan Smith, University of Wisconsin-Madison
Credit: CC0 Public Domain

The debate in sleep science has gone on for a generation. People and other animals sicken and die if they are deprived of sleep, but why is sleep so essential?

Psychiatrists Chiara Cirelli and Giulio Tononi of the Wisconsin Center for Sleep and Consciousness proposed the "synaptic homeostasis hypothesis" (SHY) in 2003. This hypothesis holds that sleep is the price we pay for brains that are plastic and able to keep learning new things.

A few years ago, they went all in on a four-year research effort that could show direct evidence for their theory.

The result, published in February 2017 in Science, offered direct visual proof of SHY. Cirelli, a professor in the University of Wisconsin's School of Medicine and Public Health, expanded on the research today (Feb. 17, 2018) at the annual meeting of the American Association for the Advancement of Science.

Striking electron-microscope pictures from inside the brains of mice suggest what happens in our own every day: Our - the junctions between nerve cells - grow strong and large during the stimulation of daytime, then shrink by nearly 20 percent while we sleep, creating room for more growth and learning the next day.

A large team of researchers sectioned the brains of mice and then used a scanning electron microscope to photograph, reconstruct, and analyze two areas of cerebral cortex. They were able to reconstruct 6,920 synapses and measure their size.

The team deliberately did not know whether they were analyzing the brain cells of a well-rested mouse or one that had been awake. When they finally "broke the code" and correlated the measurements with the amount of sleep the mice had during the six to eight hours before the image was taken, they found that a few hours of sleep led on average to an 18 percent decrease in the size of the synapses. These changes occurred in both areas of the and were proportional to the size of the synapses.

The study was big news. It was bolstered by a companion Johns Hopkins University study that analyzed brain proteins to also confirm SHY's prediction that the purpose of sleep is to scale back synapses.

For Cirelli, the study was a big gamble that paid off. But she's not resting on her laurels. Her lab is now looking at new brain areas, and at the brains of young to understand the role sleep plays in brain development.

Explore further: Sleep research high-resolution images show how the brain resets during sleep

Related Stories

Sleep research high-resolution images show how the brain resets during sleep

February 2, 2017
Striking electron microscope pictures from inside the brains of mice suggest what happens in our own brain every day: Our synapses - the junctions between nerve cells - grow strong and large during the stimulation of daytime, ...

Even in fruit flies, enriched learning drives need for sleep

June 23, 2011
Just like human teenagers, fruit flies that spend a day buzzing around the "fly mall" with their companions need more sleep. That's because the environment makes their brain circuits grow dense new synapses and they need ...

If you don't snooze, do you lose? Wake-sleep patterns affect brain synapses

October 9, 2011
An ongoing lack of sleep during adolescence could lead to more than dragging, foggy teens, a University of Wisconsin-Madison study suggests.

Mice offer a window into sleep's role in memory

March 24, 2017
Sleep provides essential support for learning and memory, but scientists do not fully understand how that process works on a molecular level. What happens to synapses, the connections between neurons, during sleep that helps ...

Slow waves may explain the brain's disconnect during dreaming

January 27, 2016
When we're dreaming, our brains appear almost as active as when we are awake, yet we remain asleep and oblivious to our surroundings.

Recommended for you

Scientists reverse a sensory impairment in mice with autism

September 25, 2018
Using a genetic technique that allows certain neurons in the brain to be switched on or off, UCLA scientists reversed a sensory impairment in mice with symptoms of autism, enabling them to learn a sensory task as quickly ...

Why it doesn't get dark when you blink

September 25, 2018
People blink every five seconds. During this brief moment, no light falls on the retina, yet people continue to observe a stable picture of the environment with no intervals of darkness. Caspar Schwiedrzik and Sandrin Sudmann, ...

Lung inflammation from childhood asthma linked with later anxiety

September 25, 2018
Persistent lung inflammation may be one possible explanation for why having asthma during childhood increases your risk for developing anxiety later in life, according to Penn State researchers.

Even mild physical activity immediately improves memory function, study finds

September 24, 2018
People who include a little yoga or tai chi in their day may be more likely to remember where they put their keys. Researchers at the University of California, Irvine and Japan's University of Tsukuba found that even very ...

Thousands of unknown DNA changes in the developing brain revealed by machine learning

September 24, 2018
Unlike most cells in the rest of our body, the DNA (the genome) in each of our brain cells is not the same: it varies from cell to cell, caused by somatic changes. This could explain many mysteries—from the cause of Alzheimer's ...

Implant helps paralysed man walk again

September 24, 2018
Five years after he was paralysed in a snowmobile accident, a man in the US has learned to walk again aided by an electrical implant, in a potential breakthrough for spinal injury sufferers.

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

michbaskett
not rated yet Feb 19, 2018
Now the trick will be to determine which synapses are most scaled back. A good assumption would be synapses that are extraneous bits of experience that were merely part of the background to what could be considered important life relevant experiences. Remove the chaff, keep the kernels.
4johnny
not rated yet Feb 20, 2018
Like evolution... branch and prune.

But another reason for sleep is glymphatic clearance.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.