youOvernight, and almost every night, something amazing will happen inside your brain. When you turn off the light switch and fall asleep, you’ll ignite the neurological equivalent of a dishwasher’s deep-clean cycle. First, the activity of billions of brain cells will begin to synchronize and oscillate between bursts of excitement and rest. Along with these “slow waves,” blood will begin to flow in and out of your brain, allowing pulses of the straw-colored cerebrospinal fluid (CSF) that usually surrounds your brain to enter and be pushed through the tissue. brain, carrying the molecular debris of the day disappear when you leave.
Most people recognize that if they don’t get enough sleep, their mood and memory will suffer the next day. But there is growing evidence implicating this “brainwashing” role of sleep in long-term brain health.
“Sleep is not just a state where things shut down. Sleep is a very active state for the brain, and it seems to be a special state for fluid flow within the brain,” says Laura Lewis, an assistant professor of biomedical engineering at Boston University. , in the US, that she has imagined this pumping process in sleeping humans.
If we don’t get enough sleep regularly, these toxic byproducts can build up, gradually increasing our risk of dementia and brain disease. We tend to get less sound sleep as we get older, making it harder to clear out debris. Fortunately, scientists are perfecting ways to stimulate this type of sleep, which could ultimately help keep our brains healthy for longer.
Doctors have long recognized the restorative properties of sleep, but it wasn’t until 2012 that Professor Maiken Nedergaard of the University of Rochester Medical Center and colleagues identified a previously unknown plumbing system in the brain that comes to life during sleep, allowing the organ to clean itself.
They found a series of tiny channels surrounding the brain’s blood vessels that allow cerebrospinal fluid to leak and be pushed through the brain tissue by the accompanying pulse of blood, and they called it “the glymphatic system,” because it is similar to the lymphatic system of the body. except that it is handled by the glial (support) cells of the brain. Having such a system is important because your neurons are extremely active during the day and produce waste that needs to go somewhere.
“Just like if you don’t have a filter in an aquarium, the fish will die in their own dirt, all this stuff builds up in the brain and needs to be removed,” says Nedergaard.
One such molecule is beta-amyloid, a toxic protein that builds up inside the brains of Alzheimer’s patients and impairs brain cell function. Nedergaard showed that significantly more beta-amyloid was removed from the brain during sleep. Other studies have found an association between lifelong sleep disruption, elevated amyloid levels, and Alzheimer’s risk.
However, Nedergaard believes that the system could be important for the removal of many other molecules; from the tau protein that accumulates in Parkinson’s disease to lactic acid, which accumulates in the brain when we’re awake and has been linked to seizures, to inflammatory molecules produced by brain-resident immune cells.
Other researchers have suggested that the glymphatic system might provide a missing link between interrupted sleep and mood disorders such as bipolar, or psychiatric illnesses including schizophrenia.
Lewis has expanded on Nedergaard’s studies by persuading human volunteers to have their brains taken while they sleep. “We saw these big waves of fluid flow that started to flood the brain about every 20 seconds and could travel quite long distances within the brain,” she says. “As soon as people woke up, this flow pattern would go away.”
This system appears to be most active during slow-wave sleep, the deepest phase of non-REM sleep that is predominant in the early morning hours.
For reasons that are not yet fully understood, people experience less of this type of sleep as they age. The glymphatic system also shows a dramatic decline in effectiveness as we enter our later years. “Your dishwasher only runs at 20% capacity,” says Nedergaard.
Deep sleep isn’t just important to keep your brain clean. We release growth hormone during it, which helps repair muscles, bones, and immune cells. Deep sleep is also considered important for memory consolidation and blood glucose regulation.
So what if scientists could find a way to restart deep sleep as we get older? Professor Penelope Lewis, a sleep researcher at Cardiff University, thinks this could be possible. Deep sleep is characterized by neurons in the brain firing together in bursts of electrical activity, followed by periods of relative inactivity, which can be visualized as “waves” on a recording of brain activity called an electroencephalogram (EEG). The Cardiff team has shown that playing a “click” sound to sleeping volunteers as they approach the peak of each oscillation can improve this neural synchrony, resulting in higher peaks and deeper valleys.
“If you keep doing that over and over again, you can increase the amount of slow-wave sleep you get, and you can also increase the extent to which memories are consolidated over the course of that sleep,” says Professor Lewis.
Extending this to older adults appears to be more challenging. Although the Cardiff team has managed to boost their slow waves, “when compared to what happens in a younger group, the effect is negligible,” he says. The researchers are now investigating whether directing the sound at a particular time point during the oscillation could have a more powerful effect.
Whether such approaches will be fruitful remains to be seen. In the meantime, there’s a lot we can do to optimize the amount of deep sleep we get, regardless of our age.
The key to focus on is sleep quality, which means avoiding coffee, alcohol, exercise, and electronic devices before bed, and keeping a dark bedroom at night. “If light comes in through the window or from the pilot lights on electronic devices, even if it doesn’t wake you up, it can push you into a lighter stage of sleep and you won’t feel as rested,” says the professor. Luis.
Sleeping may seem like a passive process, but as your consciousness recovers, the glymphatic system kicks in and helps keep your brain cool and clean. As with chores, if you miss the occasional session, no one might notice, but if you skimp too much, the clutter will gradually build up and eventually collapse.
