The gist of memory

Those of us old enough to remember the Kennedy assassination probably recall the initial announcement as if we heard it yesterday. But at the same time, it’s likely we’ll have no more recollection of extraneous details—what we were wearing, or what we were doing an hour before hearing the news—than we would for any other day in 1963.

In a new study, Caltech’s Ralph Adolphs, a professor of psychology and neuroscience, explains how the brain retains the details and gist—the central meaning—of emotional events while forgetting the chaff. The key, Adolphs says, is an area of the brain known as the amygdala. He found that patients with damage to the amygdala are unable to remember the central meaning of an emotional stimulus, even though there is nothing otherwise faulty in their memory. The research appears in this month’s Nature Neuroscience.

“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 Adolphs, the lead author of the study. “But people with damage to the amygdala fail to put this special tag on the central meaning of an emotional memory. In other words, they remember the gist of an emotional event no better than that of a neutral event.”

To test their hypothesis, Adolphs and his colleagues at the University of Iowa College of Medicine used two groups of people—a normal or control group, and a group known to have amygdala damage—and showed them a series of pictures accompanied by fabricated stories. One series involved fairly mundane episodes in which, for example, a family was depicted driving somewhere and returning home uneventfully. But the other series related a tragic event, such as the family having 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. But the group with amygdala damage possessed no better recall of the gist of the emotional story than of the mundane one. Yet both groups showed about equal ability to remember details from stories with no emotional content.

The findings, Adolphs says, suggest that the amygdala is responsible for our ability to have strong recollections of emotional events. And Adolphs says that 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.
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