Deep sleep can keep two big health problems at bay, new studies suggest
It might be worth working a little bit harder to get that much-desired, but often elusive, good night's sleep.
Deep sleep clears the mind of waste just as a "dishwasher" cleans dirty plates and glasses, just-published research suggests — and there's more.
The findings also offer insights into how sleeping pills may disrupt the "brainwashing" system — potentially affecting cognitive function for people over the long run.
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Study senior author professor Maiken Nedergaard of the University of Rochester and the University of Copenhagen said norepinephrine (a neurotransmitter and hormone) triggers blood vessels to contract — generating slow pulsations that create a rhythmic flow in the surrounding fluid to carry away waste, news agency SWNS noted.
Said Nedergaard, "It's like turning on the dishwasher before you go to bed and waking up with a clean brain. . . . We're essentially asking what drives this process and trying to define restorative sleep based on" this "glymphatic clearance."
The brain has a built-in waste removal process - the glymphatic system - that circulates fluid in the brain and spinal cord to clear out waste, according to the scientists.
The process helps remove toxic proteins that form sticky plaques linked to neurological disorders, such as Alzheimer's disease.
But the scientists indicated that what drives the system was unclear until now, according to the study.
To find clues, Nedergaard and her team looked into what happens in mice when their brains sleep, as SWNS reported of the study. The team focused on the relationship between norepinephrine and blood flow during deep sleep.
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They found that norepinephrine waves correlate to variations in brain blood volume — suggesting that norepinephrine triggers a rhythmic pulsation in the blood vessels. The researchers then compared the changes in blood volume to brain fluid flow.
The brain fluid flow fluctuates in correspondence to blood volume changes, suggesting the vessels act as pumps to propel the surrounding brain fluid to flush out waste.
Natalie Hauglund of the University of Copenhagen and the University of Oxford, the study's lead author, said, "You can view norepinephrine as [the] conductor of an orchestra."
She added, "There's a harmony in the constriction and dilation of the arteries, which then drives the cerebrospinal fluid through the brain to remove the waste products."
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Hauglund said she wanted to understand whether all sleep is created equal.
To find out, the research team administered zolpidem, a common drug to aid sleep, to mice.
They found that the norepinephrine waves during deep sleep were 50% lower in zolpidem-treated mice than in naturally sleeping mice.
Although the zolpidem-treated mice fell asleep more quickly — fluid transport into the brain dropped more than 30%, as SWNS reported.
The researchers say their findings, published in the journal Cell, suggest that the sleeping aid may disrupt the norepinephrine-driven waste clearance during sleep.
Hauglund said, "More and more people are using sleep medication, and it's really important to know if that's healthy sleep. If people aren't getting the full benefits of sleep, they should be aware of that, so they can make informed decisions."
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The research team said the findings likely apply to humans, who also have a glymphatic system, although it requires further testing.
Nedergaard added, "Now we know norepinephrine is driving the cleaning of the brain, we may figure out how to get people a long and restorative sleep."
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Meanwhile, a lack of sleep may be doing more damage than just making people groggy.
It could be sabotaging the brain’s ability to keep intrusive thoughts at bay.
Another new study, this one published in the Proceedings of the National Academy of Sciences, found that sleep deprivation weakens the brain’s defense against unwanted memories, allowing them to flood the mind, according to the New York Post.
"We show that sleep deprivation disrupts prefrontal inhibition of memory retrieval, and that the overnight restoration of this inhibitory mechanism is associated with time spent in rapid eye movement (REM) sleep," the scientists said.