Activity helps protect the brain from the strains of aging. Several different forms of mental exertion seem to provide a bit of reserve that helps hold off the forgetfulness that frequently appears in the elderly, and may limit the impact of age-related dementia. But a study released by PNAS today suggests that it's not just mental activity; physical exercise helps protect the brains of the elderly as well, and can even reverse some of the indications of aging.

The study involved a cohort of 120 older adults who were randomized into two groups: one that went on a program of three moderate-intensity aerobic workouts a week, and a second that spent an equal time doing stretching and toning exercises. Obviously, this sort of thing is difficult to do a double-blind study with—the participants presumably are aware of what their bodies are doing—but the researchers apparently kept themselves blinded to who did what when performing their analysis. MRI and memory tests were performed at the start, six months in, and when the program wrapped up after a year.

Over the course of the year, the control group that performed stretching exercises saw a small, 1.4 percent decline in the volume of the hippocampus, a brain region associated with memory. The exercising elderly, in contrast, saw the volume increase by a bit over two percent. The changes were specific to the anterior end of this structure, and weren't apparent in other areas of the brain, like the thalamus. The magnitude of the volume changes also correlated with the improvements in fitness, as measured by the change in VO 2 max. Exercisers also had higher levels of a brain growth factor called BDNF at the end of the year.

The good news for stretchers is that their volume loss didn't seem to cause problems for spatial memory; both the experimental and control groups saw their performance on the memory test improve over the course of the year. Within the group doing aerobic exercise, memory test performance and hippocampal volume changes did correlate, but given the results for those doing non-aerobic exercise, it's tough to ascribe too much importance to this finding.

The authors point out that exercise is a pretty cheap and easy-to-implement intervention, and we've got a growing population of people who could benefit from it. But they don't even discuss the possible parallels between this finding and those that suggest that mental activity can protect against the impact of aging. It's possible that the walking exercises pushed the spatial memory system more than the stretching did. Or, exercise may have simply increased the blood flow to the brain more generally, and acted a bit like neural activity in that regard. It would be nice to see these addressed in a future publication.

PNAS, 2011. DOI: 10.1073/pnas.1015950108 (About DOIs).