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 Researchers have found that during slow-wave sleep in particular -
the type of slumber sandwiched between periods of dreaming – a sort
of cleaning fluid pulses into the brain, taking out the trash as it
recedes, according to a report published in Science.
Using high speed brain imaging, the researchers were able to map out
a series of events that occur as the brain enters deep sleep and
brain waves start to slow and synchronize.
They found that the blood flow to the brain diminishes, allowing for
an influx of clear, colorless cerebrospinal fluid (CSF). That fluid
surges in and sloshes around, washing away the day's detritus of
proteins and other waste substances that might harm the brain if
they aren't cleared out.
"We haven't ever seen CSF waves on this scale in the awake brain,
suggesting that sleep involves a unique pattern of fluid flow in the
brain," said Laura Lewis, an assistant professor of biomedical
engineering at Boston University and the study's senior author.
"Previous studies in animals from other labs have shown that during
sleep, proteins such as beta-amyloid (one of two hallmark proteins
implicated in Alzheimer's disease) are cleared more rapidly from the
brain," Lewis said in an email. "Based on these studies, we wondered
why this might occur and we wanted to ask whether CSF changes during
sleep because CSF is thought to be important for waste removal."
Lewis and her colleagues suspect that poor sleep in patients with
neurological disorders might impact the tidying up process, leaving
waste materials to accumulate, eventually leading to degeneration.
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"We're running new studies to test how these CSF waves may change in
healthy aging and in neurological disorders," she said. "We're also
going to test whether this would be associated with less waste
removal from the brain during sleep in these patients."
The new research shows how the rhythmic flow of fluid during deep
sleep could be the way the brain washes away waste, Danish
researchers write in a commentary that accompanied the new study.
Understanding that process might shed a light on how disturbed sleep
could be linked to certain neurologic disorders, write Soren Grubb,
an assistant professor in the department of neuroscience at the
University of Copenhagen, and Martin Lauritzen, a professor of
clinical neurophysiology at Rigshospitalet.
"Disturbances of (slow wave sleep) commonly accompany aging, major
depressive disorders, and dementia," they note. "It will be
interesting to assess whether the CSF dynamics linked to SWS can be
used as a biomarker for disease states and whether strategies to
restore SWS can rescue brain function in neurodegeneration."
SOURCE: https://bit.ly/2pRAbZR and https://bit.ly/2CiVRkr Science,
online October 31, 2019.
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