Be honest – do you ever brag about how little sleep you get? If so, you’re not alone. Humans are the only species that seems to deliberately deprive themselves of sleep. But if you’ve ever uttered a phrase like “I’ll sleep when I’m dead,” it’s time for a wake-up call, scientists say.
Sleep is common to all species that have been studied to date.
Researchers have long known that adequate sleep is critical for good health. Insufficient sleep impairs the immune system, and is associated with everything from obesity to cardiovascular disease, stroke to cancer, depression to schizophrenia and Alzheimer’s disease. Now scientists are several steps closer to knowing how sleep keeps us healthy.
An important clue about sleep’s function surfaced in a 2013 study published in the journal Nature Neuroscienceand conducted at the University of California-Berkeley. The study, by neuroscience professor Matthew Walker and his colleagues, showed that the structural changes the brain experiences as we age damage the quality of deep sleep. This hinders the brain’s ongoing ability to store memories.
Professor Matthew Walker runs the Sleep and Neuroimaging Lab at the University of California-Berkeley. Photo by Arwen Curry.
Scientists were already aware of a connection between sleep and memory – now they are developing a working hypothesis about how the mechanism actually works.
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“It’s almost as though your learning system is like a USB stick,” Walker said. “During the day you’re acquiring lots of information rapidly.” This information is lodged in an area of the brain called the hippocampus.
But when we sleep, this data is exported to “the hard drive of our brain,” a larger storage space called the cortex.
“When we wake up the next day, our USB stick has now been cleared out, so we can start to learn new information anew,” Walker said. “We’ve refreshed our learning capacity.”
The idea that we need less sleep as we age is a fallacy, he added. It now appears that the brain is physically unable to achieve the amount of slow-wave, non-rapid-eye-movement sleep needed to consolidate memories as we grow older. By the time we’re 50 years old, non-REM sleep has reduced by half compared to when we were 18 years old. By the time we’re 70, deep sleep is down to about 5 percent.
Scientists use electrical pulses to copy the rhythm of slow-wave sleep, which declines as we age.
This research suggests that improving slow-wave sleep, which takes up about a quarter of the night, could slow the decline of memory as we age. Scientists are investigating ways to use electrical stimulation to improve deep sleep in older people by attaching electrodes to the scalp to create a mild current that mimics the pattern of slow-wave sleep.
The science of sleep has traditionally been abstract, but advances in imaging technology now allow scientists to peek inside the sleeping brain. In a groundbreaking 2013 study, researchers at the University of Rochester Medical Center injected dyes into the brains of sleeping mice, and watched in real-time as the neurons in their brains shrank dramatically by about 60 percent. This increased the spaces between the brain cells, allowing cerebrospinal fluid to easily flow through and cleanse the brain of naturally occurring toxic waste.
This photograph shows cerebrospinal fluid (in blue) rinsing toxins from the brain of a sleeping mouse. Photo courtesy of the University of Rochester Medical Center.
“It’s almost as though you’re sort of walking past one of those delightful posh hotels and during the day there’s lots of dirt that happens on the sidewalk,” said Walker. “And then at night, someone comes out with one of those pressure-jet washers and cleans it all out, so that it’s fresh and functional the next day. That’s exactly what we think is now happening during sleep at night.”
Walker’s research also suggests strong connections between sleep and creativity and emotional regulation. But with all we’ve learned about sleep, there remains much more to be discovered.
“If you think about it,” said Walker, “we’ve understood the other three main biological drives – eating, drinking and reproducing – for many tens, if not hundreds, of years. But the fourth main biological drive, common across all species that we’ve studied, which is to sleep, remains that quintessential mystery.”
One thing is clear: People are sleeping demonstrably less than they did 70 years ago. An estimated 70 million Americans suffer from some form of chronic sleep disorder, and 40 percent get less than the recommended amount of sleep – seven and a half to eight hours a night.
Contributing factors include multi-tasking, the invasion of technology in the bedroom and long commute times, which rob us of precious free hours, Walker said. But the biggest culprit may be our own attitudes.
“I think where we’re at in modern-day society is a problematic relationship with sleep,” he said.
“We know that sleep is fundamentally important at the most basic of biological levels,” he said. “But something strange has happened – sleep has received a stigma. There’s some kind of intonation which suggests that getting sufficient sleep is equivalent to being lazy. We wear this badge of sleep deprivation like some kind of honor emblem on our arm, and that’s profoundly misguided.”
