New research in rats
suggests slumbering animals devote brain power to filing away
recollections of the previous day's events. The process could
explain how some short-term memories turn into long-term ones
while others vanish.
"The general message
is that sleep is a very important thing," and not just because
it helps us rest, says study author Sidarta Ribeiro, a neurobiology
researcher at Duke University.
But one expert says
the study relies on flimsy evidence and doesn't prove the controversial
notion that our minds process memories when we aren't even conscious.
While sleep takes
up about a third of our lives -- teenagers excepted -- researchers
haven't figured out the purpose of so-called Rapid Eye Movement
(R.E.M). sleep, when dreams occur, or the deep, dreamless form
of sleep known as slow-wave.
In the latter phase,
those who are awakened "will not report a dream, but will report
thoughts," Ribeiro says.
What's happening
in the brains of humans and mammals who experience the same
back-and-forth sleep patterns? Some researchers think they know.
"In the past 30
years, particularly in the past 10 years, a lot of evidence
has accumulated that sleep is very important for learning,"
Ribeiro says. Once a memory is acquired, some experts say, sleep
helps it become properly stored away in the brain.
Ribeiro and colleagues
tested the sleep-memory theory by hooking up rats to brain scan
machines. The rats, who were living in "boring cages," were
then exposed to interesting new things -- Froot Loops (yes,
the breakfast cereal), wooden posts with spikes on them ("they
weren't supposed to like it, but they loved it," Ribeiro says),
a small brush and a golf ball mounted on a spring.
The purpose was
to intrigue the rats and then measure the reaction of their
brains to the changes in their environments. "The animals got
really excited and went on to explore the objects," Ribeiro
says. But the objects were removed after an hour so researchers
could study how the rats remembered the new experiences.
The findings appear
in the Jan. 19 online issue of the Public Library of Science.
The researchers
say they noticed that areas of the brain that were activated
when the rats explored the objects also lit up when they slept,
especially during slow-wave sleep. It's as if their brains were
echoing their earlier experiences, but at a lower level of fidelity,
Ribeiro explains. The brains of the rats may have been replaying
the day's events and deciding what to remember, Ribeiro suggests.
Jerry Siegel, a
sleep expert at the University of California at Los Angeles,
isn't convinced. He says the analysis of the brain scan is flawed,
and suggests the researchers may have "dredged out" a connection
that doesn't exist. "I'm not implying that they're being dishonest,
but it's easy to delude yourself into thinking you have something
when you don't."
He added that the
very idea that sleep contributes to learning is questionable
because people deprived of R.E.M. sleep don't forget things.
"This is the core issue: Do you really need sleep to learn things?
Many people in the field are all over the ballpark in terms
of what they claim."
Regardless of what's
really happening in the brain during sleep, Ribeiro offers some
advice that seems practical no matter what scientists believe.
"If people need to learn while studying, the best way is to
study and go to sleep, rather than study too much and stay awake,"
he says.
Indeed, another
study released this week, in the Jan. 22 issue of Nature,
linked sleep to learning. European researchers found patients
were better able to figure out a mathematical problem if they
had time to sleep on it.
More information
For more on sleep,
visit the National
Sleep Foundation or the American
Academy of Sleep Medicine.
Reference
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