We finally have
a clear understanding of the physiology of sleep itself. It also explains the genesis of brain disease
which we find is a chronic interruption of the brain’s natural housekeeping. This can lead to useful protocols and
plausibly to a cure.
It is
interesting that the system itself is unique to the brain as that is somewhat
unexpected.
I am sure this
will lead to much more knowledge.
Scientists Have
Finally Found The First Real Reason We Need To Sleep
JENNIFER WELSH OCT.
17, 2013, 2:00 PM 49,455 33
We
know we need to sleep. We know our brains and bodies work better after sleep.
But what we didn't know, until now, was why.
Scientists
have just reported the first major mechanical reason our brains need to sleep —
certain cleaning mechanisms in the brain work better when we shut the brain
down. Just like how dump trucks take to the city streets during the pre-dawn
hours because there's less traffic, our brain's cleaners also work best when there's
less going on.
"This
study shows that the brain has different functional states when asleep and when
awake," study researcher Maiken Nedergaard, of the University of Rochester said in a statement. "In fact, the restorative nature
of sleep appears to be the result of the active clearance of the by-products of
neural activity that accumulate during wakefulness."
We've
known that our brains consolidate memories during sleep and perform other
important functions. There are also benefits to the body during sleep —
resting allows our muscles, bones, and organs to repair themselves. It also keeps
our immune system healthy.
We
know that sleep has all of these benefits, but until now we didn't know
any of the specific changes that bring about these sleep benefits.
Charles
Czeisler, a sleep researcher at Harvard Medical School in Boston, told Science
Magazine's Emily Underwood that this is the "first direct experimental
evidence at the molecular level" for why we need to sleep.
The
paper was published in the journal Science on Oct. 17.
Toxic
cells
All
of our cells accumulate waste while they are working, and these waste products
can be toxic. If they aren't removed they can build up and kill our cells.
Throughout the rest of the body the lymphatic system washes these waste
products away, but the brain is cut off from these actions because of the
blood-brain barrier.
The
purple areas are the channels through which brain fluid flows, and the green
areas are the glial cells that control the flow of fluid through them.
The
team just discovered the brain's unique trash disposal system last year
— the find was published in the
journal Science Translational Medicine on Aug. 15, 2012. It works like
a plumbing system.
The
brain itself is bathed in a special clear liquid called cerebrospinal fluid,
which doesn't mix with the blood and lymph system of the rest of the body. In
the study from last year, they found that this fluid travels through special
channels and washes the brain out.
There
are two types of cells in the brain — the neurons that send signals and the
glial that keep them healthy. They found that these glial cells seem to
create these cleaning channels around the neurons.
It
washes away toxic proteins and removes them from the brain's circulatory
system. They are transferred to the general circulatory system, where the liver
can remove them.
Sleeping mice
When
mice sleep, fluid-filled channels (pale blue) between neurons expand and flush
out waste.
By
studying this newfound pathway in mice trained to sleep on a microscope, the
researchers found that this system was 10 times more active during sleep than
it was while the mice were awake.
They
injected the mice with colored toxic proteins to see the system at work — when
the mice were sleeping, these toxic proteins were removed from the brain twice
as quickly as when they were awake.
In
the new study, they found that while the brain is sleeping, the neurons
shrink by about 60% and the channels between these cells grow and fill with
fluid. The glial cells then activate their pumping system to push the
brain's cerebrospinal fluid through these extra spaces and flush out the area
around the neurons.
When
we wake, these channels squeeze shut again as the cells plump up, and the
cerebrospinal fluid is once again found mostly around the surface of the brain,
not deep inside it. While awake, this washing process acts at only about 5%
of its performance during sleep.
All
of this fluid movement is energy intensive, which is why the researchers think
it can only happen effectively during sleep. Normally, all of our brain's
energy is busy doing normal brain activities that support everything we do —
all of our movements, our thoughts, creating memories, and analyzing the
signals that come in through our senses. By shutting these processes down, our
brains are able to switch into cleaning mode.
Understanding sleep
The
toxins that this pathway removes are the kind responsible for neurodegenerative
diseases like Alzheimer's. Understanding this pathway not only helps us
understand our need for sleep, and possibly control it better with drugs that
turn it on and off, but could also lead to new ways to treat and prevent these
diseases.
The
buildup of toxic waste proteins causes brain cells to die in Alzheimer's
disease.
In
a Perspectives article in Science Magazine about the study, Suzana
Herculano-Houzel, a brain researcher at the Universidade Federal do Rio de
Janeiro, even suggested that this build up of toxins is what turns on our need
to sleep and makes us sleepy.
The
mice in the study were woken up after 60 minutes of sleep, so we don't yet know
how the amount or kind of sleep humans get affects the washing process.
While
it sounds counter-intuitive, this could even explain why some small-brained
animals need more sleep than large-brained animals. For example, bats sleep up
to 20 hours a day, while elephants sleep four. Why? Because bigger brains have
more space to store these toxins before they build up to dangerous levels and
need to be flushed.
Understanding
how "brain structure and function changes in the two different states
(sleep-wake) suggests that we can start to think about how we can manipulate
the two states," Nedergaard told Business Insider in an email.
Manipulations could include ways to put this cleaning system into
"hyperdrive" so we could sleep less, but that's way in the future.
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