Need another reason to hit the gym? New research suggests that working out builds more than just muscle. Exercise may improve memory by ramping up the creation of new brain cells.

Previous research has shown that exercise causes neuron formation in mice, so scientists at Columbia University and the Salk Institute for Biological Studies in San Diego wanted to know whether this neurogenesis also occurs in humans. Mature brains spawn new neurons in only two locations, one of which is the dentate gyrus, a region in the hippocampus linked to age-related memory decline. The researchers theorized that if exercise triggers neurogenesis in the human dentate gyrus, then exercising could improve memory and help prevent its loss in old age.

Neurogenesis is diffi cult to study, however, because direct evidence for newly born neurons can only be obtained postmortem. To look for neurogenesis in living people, the scientists needed to find a proxy—a marker indicating neuron formation that could be detected noninvasively. Comparing MRI scans of mice that had exercised regularly for two weeks with scans of sedentary mice, the researchers noticed that exercise increased blood flow in the dentate gyrus. Postmortem exams revealed that this change was, in fact, indicative of the birth of new brain cells.

The scientists then compared MRI scans of people who exercised regularly with those of
couch potatoes. Just as in the mice, the exercisers had more blood fl owing in their dentate
gyrus, suggesting that neurogenesis was also occurring there.

Finally, the scientists gave the subjects a set of cognitive tests to see if exercise actually
improved their memory. They found that the more physically fit the people were, the better they performed on hippocampus-mediated wordmemory tasks. “Physical exercise might be a very effective way to ameliorate age-related memory decline,” summarizes team member Scott Small, a neurologist at Columbia.

Small says he plans to repeat the experiments in older subjects, for whom exercise should have an even larger effect on memory.