Physical activity reorganizes the brain so that its response to stress is reduced and anxiety is less likely to interfere with normal brain function, according to a research team based at Princeton University.

The researchers report in the Journal of Neuroscience that when mice allowed to exercise regularly experienced a stressor — exposure to cold water — their brains exhibited a spike in the activity of neurons that shut off excitement in the ventral hippocampus, a brain region shown to regulate anxiety.

These findings potentially resolve a discrepancy in research related to the effect of exercise on the brain — namely that exercise reduces anxiety while also promoting the growth of new neurons in the ventral hippocampus. Because these young neurons are typically more excitable than their more mature counterparts, exercise should result in more anxiety, not less. The Princeton-led researchers, however, found that exercise also strengthens the mechanisms that prevent these brain cells from firing.