BODY & BRAIN
Sleep loss hits some brain areas hard
Scanning study reveals varied effects of lack of shut-eye
B Y RACHEL EHRENBERG
Pulling consecutive all-nighters makes
some brain areas groggier than others.
Regions involved with problem solving
and concentration become especially
sluggish, a new study reveals.
The results may lead to a better
understanding of the rhythmic nature
of symptoms in certain psychiatric or
neurodegenerative disorders, says Derk-Jan Dijk. People with dementia, for
instance, can experience “sundowning,”
or worsening symptoms at the end of
the day. More broadly, the findings, published in the Aug. 12 Science, document
the brain’s response to too little shut-eye.
“We’ve shown what shift workers
already know,” says Dijk, of the Univer-
sity of Surrey in England. “Being awake
at 6 a.m. after a night of no sleep, it isn’t
easy. But what wasn’t known was the
remarkably different response of these
The research reveals the differing
effects of the two major factors that
influence when you conk out: the body’s
roughly 24-hour circadian clock, which
helps keep you awake in the daytime
and put you to sleep when it’s dark, and
the body’s drive to sleep, which steadily
increases the longer you’re awake.
Dijk, along with Surrey colleagues and
collaborators at the University of Liege
in Belgium, studied 33 young adults who
went without sleep for 42 hours. During
this time, participants performed simple
tasks testing reaction time and memory,
and underwent 12 brain scans. Partici-
pants had another scan after 12 hours
of recovery sleep. The researchers also
measured participants’ levels of the
sleep hormone melatonin, which served
as a way to track the hands of their mas-
ter circadian clocks.
Activity in some brain areas, such as
the thalamus, a hub that connects many
other structures, waxed and waned in
sync with the circadian clock. But in other
areas, especially those in the brain’s outer
layer, the body’s drive to sleep overrode
the effects of this master clock. Brain
activity diminished in these regions as
sleep debt mounted, the scans showed.
Sleep deprivation also meddled with
performance on simple tasks, effects
influenced both by the sleep debt and the
cycles of the master clock. Performance
suffered at night but improved somewhat
during the second day, even after no sleep.
The brain’s circadian clock signal originates in a cluster of nerve cells known
as the suprachiasmatic nucleus. But it
isn’t clear where the drive to sleep comes
from, says Charles Czeisler, a sleep expert
at Harvard Medical School. The need to
sleep may grow as toxic metabolites build
up after a day’s worth of brain activity or
when certain regions run out of fuel. s
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