Deep Sleep 'Brainwashes' Us All, Study Claims

Deep Sleep 'Brainwashes' Us All, Study Claims
Slow waves of fluid wash in and out of our skull and carry away harmful excess proteins during deep sleep.

What happens to your brain when you fall asleep? New real-time brain imaging has shed more light on what happens to our brains in the dark; slow waves of fluid wash in and out of our skull and carry away harmful excess proteins during deep sleep.

Laura Lewis, a researcher at Boston University, was part of a team that demonstrated the first direct evidence of this tidal action of cerebrospinal fluid, the clear, pressurized solution that bathes our spinal cords and brains and keeps them running smoothly.

"We've known for a while that there are these electrical waves of activity in the neurons," Lewis told The Brink, Boston University's science magazine. "But before now, we didn't realize that there are actually waves in the (cerebrospinal fluid), too."

This research has broad implications for all sorts of neurodegenerative disorders, including autism, Alzheimer's, and dementia. These conditions are closely linked with sleep disturbance, and some cause buildup of protein deposits in the brain - beta-amyloid plaques, for instance - made of the harmful waste products your cerebrospinal fluid is supposed to wash away.

Slow, even waves of electromagnetic activity are a well-documented characteristic of deep sleep, Lewis said. These waves pave the way for memory consolidation and optimal brain function during the day, according to current thinking.

But the BU study, published this month in the journal Science, marks the first time those electrical oscillations have shown a connection to fluid dynamics in the brain.

The study relied on a functional MRI machine - a device that images the inside of the brain in real-time rather than producing still images as a regular MRI does. The Boston team showed slow electric waves were associated with increased oxygenated blood flowing into the brain, followed by a wave of cerebrospinal fluid.

The study participants were all aged 23 to 33, so the next round of tests will recruit older participants, Lewis said. The slow waves of deep sleep reduce in frequency as you age, which Lewis said may be connected to memory-killing plaque and metabolite buildup. Ideally, researchers will be able to understand the interplay between the electrical signals and changes in blood and fluid volume in older adults. This data will hopefully contribute to treatments and new prevention measures for age-related and other forms of dementia, Lewis said.

How Much Deep Sleep Do You Need?

Deep sleep, as defined above, only accounts for about 20% of total sleep. The largest amount of deep sleep takes place in the first half of the night, according to Melissa Conrad Stöppler, MD, a pathologist and MedicineNet author/editor.

Individuals vary greatly in their need for sleep in general; there are no established criteria to determine exactly how much sleep a person needs. Eight hours or more may be necessary for some people, while others may consider this to be too much sleep, Dr. Stöppler said.

The National Institutes of Health (NIH) suggests that most average adults need about 7 to 9 hours of sleep each night. Newborn babies, by contrast, sleep from 16 to 18 hours a day. Preschool-aged children typically sleep between 10 and 12 hours a day. Older, school-aged children and teens need at least 9 hours of sleep a night. Women in the first trimester of pregnancy have been observed to need a few more hours' sleep than is usual for their age, Dr. Stöppler said.

Physiologically, sleep is a complex process of restoration and renewal for the body. Scientists still do not have a definitive explanation for why humans have a need for sleep, Dr. Stöppler said.

We do know that sleep is not a passive process or "switching off" of body functions; sleep is believed to be important in many body processes, Dr. Stöppler said. It allows us to process experiences and consolidate memories. It is also clear that sleep is essential, not only for humans but for almost all animals.

The importance of sleep is underscored by the symptoms experienced by those suffering from sleep problems, Dr. Stöppler said. People suffering from sleep disorders do not get adequate or restorative sleep, and sleep deprivation is associated with a number of both physical and emotional disturbances.

Source: MedicineNet Health News.

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