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Key to False Memories Uncovered

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Duke Health News 919-660-1306

DURHAM, N.C. – Duke University Medical Center
neuroscientists say the places a memory is processed in the
brain may determine how someone can be absolutely certain of a
past event that never occurred.

These findings could help physicians better appreciate the
memory changes that accompany normal aging or even lead to
tools for the early diagnosis of Alzheimer's disease, according
to Duke neuroscientist Roberto Cabeza, Ph.D.

Information retrieved from memory is simultaneously
processed in two specific regions of the brain, each of which
focuses on a different aspect of an past event. The medial
temporal lobe (MTL), located at the base of the brain, focuses
on specific facts about the event. The frontal parietal network
(FPN), located at the top of the brain, is more likely to
process the global gist of the event.

The specific brain area accessed when one tries to remember
something can ultimately determine whether or not we think the
memory is true or false, the researchers found.

"Human memory is not like computer memory -- it isn't
completely right all the time," said Cabeza, senior author of a
paper appearing in the Journal of Neuroscience. "There are many
occasions when people feel strongly about past events, even
though they might not have occurred."

Cabeza wanted to understand why someone could have such
strong feelings of confidence about false memories. In his
experiments, he scanned the brains of healthy volunteers with
functional MRI as they took well-established tests of memory
and false memory. Functional MRI is an imaging technique that
shows what areas of the brain are used during specific mental
tasks.

During the brain scans, Cabeza found that volunteers who
were highly confident in memories that were indeed true showed
increased activity in the fact-oriented MTL region.

"This would make sense, because the MTL, with its wealth of
specific details, would make the memory seem more vivid,"
Cabeza said. "For example, thinking about your breakfast this
morning, you remember what you had, the taste of the food, the
people you were with. The added richness of these details makes
one more confident about the memory's truth."

On the other hand, volunteers who showed high confidence in
memories that turned out to be false exhibited increased
activity in the impressionistic FPN. The people drawing from
this area of the brain recalled the gist or general idea of the
event, and while they felt confident about their memories, they
were often mistaken, since they could not recall the details of
the memory.

These findings, coupled with the findings of other studies,
can help explain what happens to the human brain as it ages,
Cabeza said.

"Specific memories don't last forever, but what ends up
lasting are not specific details, but more general or global
impressions," Cabeza said. "Past studies have shown that as
normal brains age, they tend to lose the ability to recollect
specifics faster than they lose the ability recall impressions.
However, patients with Alzheimer's disease tend to lose both
types of memories equally, which may prove to be a tool for
early diagnosis."

Cabeza's colleague for this research was Hongkeun Kim at
Daegu University in South Korea. The research was supported by
the National Institutes of Health and Daegu University.

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