| It has long been assumed that
sleep deprivation can play havoc with our emotions.
This is notably apparent in soldiers in combat zones,
medical residents and even new parents. Now there's a
neurological basis for this theory, according to new
research from the University of California, Berkeley,
and Harvard Medical School.
In the first neural investigation into what happens
to the emotional brain without sleep, results from a
brain imaging study suggest that while a good night's
rest can regulate your mood and help you cope with the
next day's emotional challenges, sleep deprivation does
the opposite by excessively boosting the part of the
brain most closely connected to depression, anxiety and
other psychiatric disorders.
"It's almost as though, without sleep, the brain had
reverted back to more primitive patterns of activity, in
that it was unable to put emotional experiences into
context and produce controlled, appropriate responses,"
said Matthew Walker, director of UC Berkeley's Sleep and
Neuroimaging Laboratory and senior author of the study,
which will be published today (Monday, Oct. 22) in the
journal Current Biology.
"Emotionally, you're not on a level playing field,
"Walker added.
That's because the amygdala, the region of the brain
that alerts the body to protect itself in times of
danger, goes into overdrive on no sleep, according to
the study. This consequently shuts down the prefrontal
cortex, which commands logical reasoning, and thus
prevents the release of chemicals needed to calm down
the fight-or-flight reflex.
If, for example, the amygdala reacts strongly to a
violent movie, the prefrontal cortex lets the brain know
that the scene is make-believe and to settle down. But
instead of connecting to the prefrontal cortex, the
brain on no sleep connects to the locus coeruleus, the
oldest part of the brain which releases noradrenalin to
ward off imminent threats to survival, posing a volatile
mix, according to the study.
The study's findings lay the groundwork for further
investigation into the relationship between sleep and
psychiatric illnesses. Clinical evidence has shown that
some form of sleep disruption is present in almost all
psychiatric disorders.
"This is the first set of experiments that demonstrate
that even healthy people's brains mimic certain
pathological psychiatric patterns when deprived of
sleep, "Walker said."Before, it was difficult to
separate out the effect of sleep versus the disease
itself. Now we're closer to being able to look into
whether the person has a psychiatric disease or a
sleep disorder."
Using functioning Magnetic Resonance Imaging (fMRI),
Walker and his team found that the amygdala, which is
also a key to processing emotions, became hyperactive
in response to negative visual stimuli - mutilated
bodies, children with tumors and other gory images -
in study participants who stayed awake for 35 hours
straight. Conversely, brain scans of those who got a
full night's sleep in their own beds showed normal
activity in the amygdala.
"The emotional centers of the brain were over 60
percent more reactive under conditions of sleep
deprivation than in subjects who had obtained a normal
night of sleep," Walker said.
The team studied 26 healthy participants aged 18 to
30, breaking them into two groups of equal numbers of
males and females. The sleep-deprived group stayed
awake during day 1, night 1 and day 2, while the
sleep-control group stayed awake both days and slept
normally during the night. During the fMRI brain
scanning, which was performed at the end of day 2,
each was shown 100 images that ranged from neutral to
very negative. Using this emotional gradient, the
researchers were able to compare the increase in brain
response to the increasingly negative pictures.
Since 1998, Walker, an assistant professor of
psychology at UC Berkeley and a former sleep
researcher at Harvard Medical School, has been
studying sleep's impact on memory, learning and brain
plasticity.
During his research, he was struck with the
consistency of how graduate students in his studies
would turn from affable, rational beings into what he
called "emotional JELL-O" after a night without sleep.
He and his assistants searched for research that would
explain the effect of sleep deprivation on the
emotional brain and found none, although there is
countless anecdotal evidence that lack of sleep causes
emotional swings.
"You can see it in the reaction of a military
combatant soldier dealing with a civilian, a tired
mother to a meddlesome toddler, the medical resident
to a pushy patient. It's these everyday scenarios that
tell us people don't get enough sleep." Walker said.
The body alternates between two different phases of
sleep during the night: Rapid Eye Movement (REM), when
body and brain activity promote dreams, and Non-Rapid
Eye Movement (NREM), when the muscles and brain rest.
"All signs point to sleep doing something for
emotional regulation and emotional processing," Walker
said. "My job now is to figure out what kind of
sleep."
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