Sleep May Help Restore Memories
Wed Oct 8, 1:22 PM ET Add Top Stories - AP to My Yahoo!
By RICK CALLAHAN, Associated Press Writer

In a finding that backs up motherly advice to get a good night's
sleep, scientists have found that peaceful slumber apparently
restores memories that were lost during a hectic day.

It's not just a matter of physical recharge. Researchers say sleep
can rescue memories in a biological process of storing and
consolidating them deep in the brain's complex circuitry.

The finding is one of several conclusions made in a pair of studies
that appear in Thursday's issue of the journal Nature that look at
how sleep affects the memory-recording processes, and perhaps
safeguards them.


Researchers who conducted the experiments said the results may
influence how students learn, and someday could be incorporated into
treatments for mental illnesses involving memories, such as post-
traumatic stress disorder.


However, other scientists who were not involved in the experiments
said additional research is needed into the sleep-memory connection.


In separate studies, scientists at the University of Chicago and the
Harvard Medical School (news - web sites) trained college-age people
to perform specific tasks, then tested them to see how much they
recalled after either a night's sleep or several hours awake.


The University of Chicago study found that test subjects who listened
to a voice synthesizer's murky speech understood more words after a
night of sleep than counterparts who were tested just hours after the
training, with no sleep.


"We all have the experience of going to sleep with a question and
waking up with the solution," said Daniel Margoliash, a professor of
neurobiology at the University of Chicago.


Margoliash, who worked with colleagues Howard Nusbaum and Kimberly
Fenn, said it could be that a person acquires so many memories each
day that some details are lost in that jumble — but that the brain
sorts and reorganizes the memories during sleep.


Or, memories could actually be lost during the day, he said, but
reconstituted by the brain during sleep by some process that taps
into the general rules the test subjects learned in their voice-
recognition training.


James L. McGaugh, director of the Center for the Neurobiology of
Learning and Memory, at the University of California at Irvine, said
the voice recognition training is similar to learning a new language
and is therefore more complex than being taught to repeat a simple
task. In the tests, the subjects never heard the same synthesized
word twice.


"These are highly interesting findings that add additional
information concerning the affects of sleep on memory," he
said. "This takes it to a new level."


Still, McGaugh said further experiments are needed to assess a number
of factors that could have influenced the outcomes.


For example, he said the people trained late at night may have
performed better because they went to sleep not long after their
training, while their morning trained counterparts were exposed to an
entire day of memories before being tested.


In that study, one group was trained at 9 a.m., then tested 12 hours
later, while a second group was trained at 9 p.m. and then tested the
next morning after a night's sleep.


The researchers found that while the people tested at night
experienced a 10 percentage point improvement over their pre-training
test, those who had a night's sleep had a 19 percentage point
improvement over their pre-training test.


In the second study, Harvard Medical School scientists trained 100
subjects ages 18-27 to perform finger-tapping sequences similar to
learning piano scales. Their ability to repeat those sequences was
then tested at various intervals, including after one and two nights
of sleep.


The researchers found evidence that memories are consolidated in
three stages in a process similar to storing data on a computer's
hard drive. The second stage requires sleep, which the Harvard team
also found sharpened the subject's performance the next day.

However, when subjects briefly rehearsed a finger-tapping sequence
they had learned the previous day just before learning a second
exercise, their accuracy on the first sequence suffered when they
tried to repeat it on the third day.

But they performed the second exercise reliably — suggesting
that "not all memories are equal," and the order in which they are
learned may be important, said McGill University psychologist Karin
Nader, who reviewed both Nature studies.

___

On the Net:

Nature journal: http://www.nature.com


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