calm. Especially if you do it during the daytime
when they are supposed to be sleeping, and they
are warm and you give them sugar water. They’re
The day of the experiment, the scientists made
a hole in the mice’s skulls, placed a cover over it
and injected a dye to measure cerebrospinal fluid
in the brain. During sleep, the spaces between
the brain cells widened by about 60 percent and
allowed more fluid to wash through, taking the
metabolic debris, including A-beta, with it.
“It’s like the dishwasher turned on,” Nedergaard
says. She named this phenomenon the “glymphatic
system” because it appears to be controlled by glial
cells, brain cells that help insulate neurons and
perform much of the brain’s routine maintenance
work (SN: 8/22/15, p. 18).
Similar observations of cerebrospinal fluid circulation have been carried out in people, but with
less invasive ways of measuring. In one, researchers from Oslo University Hospital, Rikshospitalet
compared 15 patients who had a condition called
normal pressure hydrocephalus, a kind of dementia caused by buildup of cerebrospinal fluid in the
cavities of the brain, with eight people who didn’t
have the condition.
The researchers used a tracer for cerebrospinal
Don’t snooze, you lose?
fluid and magnetic resonance imaging to measure
the flow over 24 hours. Immediately after a night’s
sleep, cerebrospinal fluid had drained in healthy
people but lingered in the patients with dementia,
the researchers reported in Brain in 2017.
The central question — the one that doctors really
want to answer — is whether better sleep could
treat or even prevent Alzheimer’s. To try to figure
this out, Bendlin and her Wisconsin colleagues
are now studying people with sleep apnea. People
with that condition stop breathing during the night,
which wakes them up and makes for a lousy night’s
sleep. A machine called a CPAP, short for continuous positive airway pressure, treats the condition.
“Once people start treatment, what might we
see in the brain? Is there a beneficial effect of
CPAP on markers of Alzheimer’s?” Bendlin won-
ders. “I think that’s a big question because the
implications are so large.”
A study reported in Neurology in 2015 offers
a reason to think CPAP might help. Using data
from almost 2,500 people in the Alzheimer’s
Disease Neuroimaging Initiative, researchers at
the New York University School of Medicine found
that people with sleep disorders like obstructive
sleep apnea showed signs of mild cognitive prob-
lems and Alzheimer’s disease at younger ages than
those who did not. But for those who used CPAP,
onset of mild cognitive problems was delayed.
“If we find out that sleep problems contribute
to brain amyloid — what that really says is there
may be a window to intervene,” Bendlin says. And
the solution — more attention to sleep — is one
prescription with no side effects. s
s Yumna Saeed and Sabra M. Abbott. “
Circadian disruption associated with Alzheimer’s
Disease.” Current Neurology and Neuroscience
Reports. April 2017.
Flow of cerebrospinal
fluid in a mouse’s brain
is much higher during
sleep (left, red) than
when the animal is
awake (right, green).
Go with the flow
One way the brain might
clear out waste, including
amyloid-beta, is via circulation of cerebrospinal and
interstitial fluids. Fluid flows
through the spaces in the
brain, bathing neurons and
eventually carrying debris
out of the brain toward the
liver. Studies suggest that
this “glymphatic” circulation
increases during sleep.
SOURCE: M. NEDERGAARD/SCIENCE 2013