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Thanks
for the Memories? Sleep May Deserve Some Credit
Brain Patterns During Learning, REM Sleep Are
Similar |
 By
Neil Osterweil
WebMD Medical News
Reviewed by Dr. Jacqueline Brooks
When Mom said to get a good night's sleep before
that big exam, she may have been right -- again.
Belgian researchers used imaging technology to peer
into the brains of sleeping volunteers and found
evidence that the "REM" (rapid eye movement)
phase of sleep may be a form of after-hours memory
processing and storage.
Sleep researchers have known for nearly 50 years
that REM sleep, which occurs several times a night
in most people, is a period of intense activity,
during which a sleeper's eyes dart rapidly around
beneath his closed eyelids as if he were watching
an invisible tennis match, and his brain churns
away like a Porsche in overdrive. REM sleep is also
when most long, active dreams occur. People who
are woken during the REM phase often report being
interrupted in the middle of a dream, which they
are usually able to recall with clarity.
Although we spend a third of our lives asleep and
that's not counting the time we spend snoozing on
the hammock or dozing in front of the tube the functions
of REM, dreams, and even sleep it self are still
largely unknown. But as researchers report in the
August issue of the journal Nature Neuroscience,
REM may be a way for the brain to recall and chew
over newly formed memories before filing them away
in the darker recesses of the brain somewhat akin
to setting the computer to do a file reorganization
and hard-drive backup overnight.
Pierre Maquet, PhD, and colleagues from the Universities
of Liege and of Libre de Bruxelles in Belgium, and
Trent University in Peterborough, Ontario, sat volunteers
down at computers to perform unfamiliar tasks. They
were told to press the correct pad on a keyboard
in response to something appearing on the screen.
The researchers looked at reduction in reaction
time as a measure of whether the volunteers were
learning a new skill. They found that reaction times
tended to improve after a night's sleep and that
accuracy did not deteriorate, suggesting that some
type of memory processing or consolidation had occurred
while the volunteers dreamed on.
The volunteers performed their assigned tasks while
being evaluated with a type of brain scanning device
called a positron-emission tomography (PET) scanner.
PET scans measure blood flow in the brain, and in
this study served as a means of mapping out the
geography of learning, by showing which parts of
their brains require more blood and therefore, presumably,
are being activated by a new stimulus.
The researchers then examined the pattern of brain
activity of a group of trained volunteers as they
slept inside the PET scanner, and compared the results
with those for untrained volunteers. They found
that volunteers who had learned the task before
turning in had patterns of brain activation during
REM that were similar to those that occurred when
they were performing the task hours earlier. The
patterns during REM were also significantly different
between the trained and the untrained volunteers.
The researchers suggest that REM sleep may contribute
to the storage or consolidation of memories by recalling
and replaying them during a period of high activity
of certain brain chemicals, called neurotransmitters
that are known to promote brain activity. The increased
neurotransmitter activity could in turn strengthen
synapses - small gaps in brain circuitry that act
as bridges or junction boxes for sending electrical
signals from one nerve ending to another.
"What they have found is perfectly reasonable,
and it essentially elaborates on work that has been
done with rats," says dreams researcher J.
Lee Kavanau, PhD, professor emeritus of organismic
biology, ecology, and evolution at UCLA.
Kavanau points to recent studies showing that when
rats learn to find their way around a new environment
and then settle in for a siesta, the patterns of
activity in their feverish little brains that were
observed as they explored are replayed while they
sleep.
Sleep researchers also know that reduced REM time
can lead to memory impairment and learning problems,
so perhaps college kids should forgo strings of
all-night study sessions in favor of some shut-eye.
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