In healthy adults, the hippocampus  a part of the brain important to the formation of memories  begins to atrophy around 55 or 60. Now psychologists are suggesting that the hippocampus can be modestly expanded, and memory improved, by nothing more than regular walking.

In a study published on Jan. 31 in The Proceedings of the National Academy of Sciences, researchers randomly assigned 120 healthy but sedentary men and women (average age mid-60s) to one of two exercise groups. One group walked around a track three times a week, building up to 40 minutes at a stretch; the other did a variety of less aerobic exercises, including yoga and resistance training with bands.

After a year, brain scans showed that among the walkers, the hippocampus had increased in volume by about 2 percent on average; in the others, it had declined by about 1.4 percent. Since such a decline is normal in older adults, “a 2 percent increase is fairly significant,” said the lead author, Kirk Erickson, a psychologist at the University of Pittsburgh. Both groups also improved on a test of spatial memory, but the walkers improved more.

While it is hard to generalize from this study to other populations, the researchers were delighted to learn that the hippocampus might expand with exercise. “And not that much exercise,” Dr. Erickson pointed out.