Well Tara Parker-Pope on Health by Danielle Ofri, M.D.
Why, as we grow older, do we forget where we parked the car, and could exercise sharpen our recall? Those questions, of considerable interest to any of us who possess a brain as well as those with cars, is motivating a series of remarkable new experiments by researchers at Johns Hopkins University and the Center for the Neurobiology of Learning and Memory at the University of California, Irvine, during which young and older volunteers watch pictures flash onto a screen, while the scientists watch their brains.
Creating and accessing memories are complicated processes, with the specific physiological mechanisms still largely unknown. But, using brain scans, neuroscientists already have established that quite a bit of the electrical activity and blood flow associated with memory processing occurs in the dentate gyrus, a part of the brain within the hippocampus, a larger portion of the brain known to be involved with learning and thinking.
It turned out that young adults were quite good at differentiating the images into those that were brand-new, already seen or similar to but not exactly the same as earlier pictures (a baby grand piano instead of a full grand, for instance). The brain activity in each young person’s dentate gyrus responded accordingly. “There would be a lot of activity when young people saw either new or similar objects,” said Michael A. Yassa, an assistant professor of psychological and brain sciences at Johns Hopkins and lead author of the study. The young people’s brains were, this activity indicates, learning and storing the new images as new images, even when they were quite similar to the images they had seen before.Specifically, the volunteers, wearing head sensors, were shown a series of pictures of everyday objects, like computers, telephones, pineapples, pianos and tractors, and asked to press a button indicating whether each object typically was found indoors or outside. They were not asked to remember the images. But later they were shown another set of images and asked whether they remembered seeing that specific photo before or a similar photo, or whether the picture was completely new to them. The researchers tracked brain activity throughout both tasks.
The brains of the older volunteers, ages 60 to 80, though, did not seem to work as well. Their dentate gyri typically showed far less activity when they were shown a similar but not identical image. Their brains apparently did not create a completely new memory to correspond to the slightly different picture, so that the photo of the baby grand registered as no different than the one of the full grand. In turn, they usually referred to pictures that were similar but not identical to ones they’d seen earlier as “old” photos.
None of these lapses were severe. But they do indicate, Dr. Yassa said, that the older adults were less successful at pattern separation, or the ability to differentiate between things that are quite similar.
There are many different types of memory processing, of course, but one of the more important for everyday functioning is pattern separation. “Take breakfast,” Dr. Yassa said. Most of us follow a routine and eat much the same thing at the same time for breakfast most days, he said. But each morning’s meal is unique and should produce a unique set of memories. “You need to be able to separate those memories and keep them apart,” Dr. Yassa said. “Otherwise they can override one another and confuse things.”
Aging, Dr. Yassa’s work suggests, blunts our ability to separate yesterday’s corn flakes from last Wednesday’s raisin bran, or today’s parking slot from Monday’s. The problem is, in part, structural, he believes. In a separate part of his experiments, using newly developed M.R.I. scanning technology, he found that the dentate gyrus in many of the older volunteers was not connected as robustly to the rest of the brain as in young people. Messages did not flow as easily from elsewhere in the brain to the dentate gyrus memory center, and vice versa.
But there is hope, Dr. Yassa said. “Exercise is one of the things that might directly change this process,” he said. In other experiments, exercise has been found to jump-start neurogenesis, or the creation of new brain cells, especially in the dentate gyrus, he said, potentially improving that area’s health and functioning.
The process has worked in rodents. A heartening study from last year conducted at the National Institute on Aging found that mice that voluntarily scampered on running wheels displayed an “enhanced” ability to separate closely spaced squares on a display screen, the animal equivalent of pattern recognition, compared with sedentary animals. The runners also had far more new neurons in their dentate gyri than the mice that didn’t run. The extent to which exercise improves pattern recognition processing in people is still unknown. But Dr. Yassa is including measures of physical fitness and exercise history as part of his continuing research. The results so far look encouraging, he said.
“What I’d say for now is that you can’t go wrong by exercising,” he said. “We don’t know if it can reverse” any damage if you already have memory slips. But there are indications that it might slow or possibly prevent memory deterioration, if you begin exercising early enough — meaning that, among the many benefits of a health club membership, your workout may help you to recall where in the gym parking lot you left your car.
