In the 1973 film "The Way We Were," Barbra Streisand sings a haunting ballad about memories and aging. "What's too painful to remember, we simply choose to forget," the song goes.
Now, research suggests that the song was essentially right, and illustrates just how the brain manages to dismiss negative memories but retain the positive ones as we get older.
A team of researchers from Duke University and University of Alberta took two groups of volunteers - one in their mid-20s, one in their 70s - and showed them photos that were either neutral or very negative, depicting such things as mutilated bodies or sick children. Later, the participants were unexpectedly asked to recall the images. The older group had a harder time recalling the negative images than the younger group, and brain scans revealed the differences in brain activity between the two groups.
The study - which points to possible ways to improve memory in aging adults - appears in the January issue of Psychological Science. Peggy St. Jacques, the Duke University graduate student in psychology and cognitive neuroscience who is the lead author, said there are primal reasons why seniors tend to take a dim view of unpleasant memories.
"As we age, we have a more limited perspective of the time we have left," she said, "so we may focus more on things that increase our emotional well-being."
In practical terms, that might mean that an older person's memory of the family reunion will focus on the delights of the grandchildren playing on the lawn, not the shouting match at lunch over their divorcing parents' custody battle. Or on the glow of the sunset over the dunes, not the litter scattered across the sand.
"Not everything that happens with aging is negative," says Dr. Gene D. Cohen, director of the center on aging, health and humanities at George Washington University.
There are related advantages, he notes: People develop "longer fuses," and are better able to control and regulate anger and other negative emotions. "The highs may be just as high, but the lows are not as low," he said. And people with certain conditions such as social phobias often find their illnesses diminishing with age, Cohen said.
St. Jacques's study is not the first to show how the aging brain filters out the negative.
Other scientists, most notably Stanford University psychologist Laura Carstensen, have also demonstrated that seniors tend to remember more positive than negative events. And still other research has revealed that in brain scans the amygdala, the brain's emotion detector, lights up equally intensely in young and old while viewing positive events, yet does not light up as brightly or as long in older people when they view negative images.
But St. Jacques's study, while small in the number of participants - there were 15 people in each group - is the first to trace the pathway of an emotional memory in the brain as it is formed, and to look at the age-related differences.
Brain scans taken while the participants viewed the pictures revealed that while both groups had similar activity in the brain's emotional center, they differed when it came to how the centers interacted with the rest of the brain. Younger people were connecting more with another region of their brain typically associated with learning and memory, known as the hippocampus, while older adults relied more on a portion involved in controlling emotions, called the frontal cortex.
That control center, said St. Jacques, helps seniors filter out or reappraise unpleasant images as they form memories.
The brain's forget-the-bad-retain-the-good memory function appears gradually as we age. One 2005 study by Carstensen, the Stanford psychologist, showed that the phenomenon was only slightly more pronounced in participants, age 41-53, than in the younger volunteers. But the differences grew more striking for the 65 to 80 group. The elders were only able to recall about half of the negative and neutral images compared to their young counterparts.
Such research, said Molly V. Wagster, a senior brain scientist at the National Institute on Aging, offers tantalizing clues for developing drugs and designing treatments to improve memory in aging adults.
"With this, we come closer to better understanding the changes in the brain with age, and how we can capitalize on that," Wagster said.
For instance, she said, the latest finding reinforces the hypothesis that older adults may do a better job recalling information if it is delivered with emotionally pleasant or positive images.
One potential area for future study, said St. Jacques, is to investigate whether the age-related differences in the brain that scientists witnessed in the latest study are the same when older adults are asked to recall not recent memories, but those from years earlier, especially from their childhood or during young adulthood. Those memories would have been formed when the connections were more intense between the brain's emotional center and the region involved with learning and memory, which would suggest that they might be more easily remembered, even the negative ones.
But St. Jacques isn't sure.
"Older adults might also engage emotional regulation processes that would dampen their emotional response when they retrieve these very remote, negative memories," she said. "Thus, we might expect there to be similar age-related differences" here, too.
Kay Lazar can be reached at firstname.lastname@example.org.