Medical: Taking a nap helps delete brain e-mails
Study suggests naps can be best memory tools
Scripps Howard News Service
Scientists continue to find new clues to how the brain processes information and remembers certain things.
And it turns out that one of the best memory tools around may be a nap.
Researchers at the University of California, Berkeley, reported earlier this year that a group of student volunteers who took a 90-minute, mid-afternoon nap markedly outperformed a similar group who got no nap when both engaged in a round of learning exercises later in the day.
Scientists have known for years that sleep deprivation makes the mind sluggish and less able to process new information. Severe insomnia has been even been shown to shrink the volume of key brain areas.
Specifically, sleep seems to recharge the hippocampus, a region of the brain that helps store fact-based memories before they're consolidated in the neocortex. Studies of mice, fruit flies and humans have documented the pathways to memory consolidation.
Matthew Walker, an assistant professor of psychology who has been studying the process in humans since 2007, said the latest test — which also monitors the depth of sleep in the brains of the napping students — found that they mostly were in a middle stage between deep sleep and rapid-eye-movement sleep (the dream stage).
Researchers had wondered why humans spend at least half their sleeping hours in this middle stage, and the new findings suggest an answer: The brain uses this break to refresh short-term memory.
"It's as though the e-mail inbox in the hippocampus is full and, until you sleep and clear out those fact e-mails, you're not going to receive any more mail," Walker said.
Another recent study, carried out at the University of Iowa, offers further evidence of the importance of a functional hippocampus.
The test involved five patients with damage to the hippocampus that left them unable to form new memories. Their amnesia is similar to the forgetfulness seen in many patients at the onset of Alzheimer's disease.
Researchers, led by graduate student Justin Feinstein, had each patient view a 20-minute clip of a happy or sad movie on separate days. The movies triggered appropriate emotions in each patient — laughter or tears.
About 10 minutes after watching the movie, the researchers quizzed patients about what they'd just watched. While a healthy person would be able to recall about 30 details from the film, the amnesic patients recalled very little. One patient couldn't remember a single detail.
But when the amnesic patients were asked about their emotional feelings following the memory test, the impact of the films lingered long after the details of the film were lost.
"Both emotions lasted well beyond their memory of the films," Feinstein said.
The findings represent an important message for caregivers and loved ones of Alzheimer's patients, he said. "A simple visit or phone call from family members might have a lingering positive influence on a patient's happiness," even though he or she is likely to quickly forget what brought about their happiness.
At the same time, Feinstein cautioned that neglect or negativity from home or nursing-home caregivers might leave a patient feeling sad and frustrated, even though there's no memory of why they feel that way.
If the hippocampus helps record facts, a more basic brain structure, the amygdale, records fear. The brain's fear center arouses our basic inclinations to fight or run, but recent studies show that this and other parts of the brain are able to make sophisticated distinctions about which fears are important to survival and thus need to be easily retrieved.
However, another report shows that some fears are not learned, but may be genetically inborn.
The experiment, published this week in the journal Current Biology, compared the reactions of children with a genetic condition known as Williams syndrome and those in a group without the condition.
Youngsters with the syndrome have unusually open, friendly natures because they lack the sense of fear that people feel in certain social situations.
But in the test set up by German and French researchers, the children with Williams syndrome also demonstrated they lack something else — racial stereotypes. The two groups of children were shown images of various people and then were asked to assign positive or negative features to those pictured.
The control group made typical assumptions both for race and gender. The Williams group showed no evidence of racial bias, but did make stereotypical judgments based on gender. This suggests that different forms of stereotyping are controlled by different parts of the brain.
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