Physical activity adapts the brain so that its response to stress is reduced and anxiety is less likely to interfere with brain function, U.S. researchers say. Senior author Elizabeth Gould of Princeton University said members of her laboratory pinpointed brain cells and regions important to anxiety regulation that might help scientists better understand and treat human anxiety disorders. The study, published in the Journal of Neuroscience, found 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, Gould said. However, the Princeton researchers found exercise also strengthens the mechanisms that prevent these brain cells from firing. \"Understanding how the brain regulates anxious behavior gives potential clues about helping people with anxiety disorders,\" Gould said. \"It also tells us something about how the brain modifies itself to respond optimally to its own environment.\" The research was part of the graduate dissertation for first author Timothy Schoenfeld, now a postdoctoral fellow at the National Institute of Mental Health, as well as part of the senior thesis project of co-author Brian Hsueh, now a doctoral student at Stanford University.