Mar. 10, 2005 PASADENA, Calif. -- Those of us who are old enough to remember the Kennedy assassination are usually able to remember the initial announcement almost as if it's a movie running in our heads. That's because there is a well-known tendency for people to have enhanced memory of a highly emotional event, and further, a memory that focuses especially on the "gist" of the event.
In other words, people who remember the words "President Kennedy is dead" will remember the news extraordinarily well. But at the same time, they will likely have no more recollection of extraneous details such as what they were wearing or what they were doing an hour before hearing the news than they would for any other day in 1963. Neurobiologists have known both these phenomena to be true for some time, and a new study now explains how the brain achieves this effect.
In the new study, researchers from the California Institute of Technology and the University of Iowa College of Medicine show how the recollections of gist and details of emotional events are related to specific parts of the brain. In an article appearing in this month's Nature Neuroscience, the authors report that patients with damage to an area of the brain known as the amygdala are unable to remember the gist of an emotional stimulus, even though there is nothing otherwise faulty in their memory. The study shows that the amygdala somehow focuses the brain's processing resources on the gist of an emotional event.
"During a highly emotional event, like the Kennedy assassination, 9/11, or the Challenger accident, you remember the gist much better than you would remember the gist of some other neutral event," says Ralph Adolphs, a professor of psychology and neuroscience at Caltech and lead author of the study. "But people with damage to the amygdala have a failure to put this special tag on the gist of emotional memories. In other words, they remember the gist of an emotional event no better than the gist of a neutral event."
To test their hypothesis, Adolphs and his colleagues at the University of Iowa College of Medicine showed a group of normal control subjects and a group of test subjects known to have amygdala damage a series of pictures accompanied by fabricated stories. One type of series involved fairly mundane episodes in which, for example, a family was depicted driving somewhere and returning home uneventfully. But in the other series, the story would relate a tragic event, such as the family having been involved in a fatal auto accident on the way home, accompanied with gruesome pictures of amputated limbs.
As expected, the normal control subjects had enhanced recall of the emotional stories and pictures, and far more vague recall of the mundane stories. The test subjects with amygdala damage, however, possessed no better recall of the gist of the emotional story than of the mundane stories. On the other hand, both the control group and the group with amygdala damage showed about equal ability to remember details from stories with no emotional content.
The findings suggest that the amygdala is responsible for our ability to have strong recollections of emotional events, Adolphs says. Further study could point to how the amygdala is involved in impaired real-life emotional memories seen in patients with post-traumatic stress disorder and Alzheimer's disease, he adds.
The other authors of the article are Daniel Tranel and Tony W. Buchanan, both of the University of Iowa College of Medicine's Department of Neurology.
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