Physical activity contributes to a plethora of benefits. From preventing diseases to increasing endorphins, and lowering stress, researchers are constantly learning about its benefits. Now, a new study finds that it not only lowers stress but it can cause the brain to become more resistant to it too.

Researchers found that the brains of mice that were physically active were able to reorganize in a way that reduced its response to stress and anxiety. They wanted to see why previous research says that new, more excitable neurons in the ventral hippocampus, which grow as a result of physical activity, are supposed to cause more anxiety. However, they found that physical activity also strengthens mechanisms in the brain that prevent the neurons from firing.

They discovered this after they ran tests on two groups of mice in which one group was allowed unlimited access to a running wheel and the other group wasn't. After six weeks, they exposed the mice to cold water for a short period of time.

They found that the cold water incited an increase in immediate early genes — activated rapidly in response to stimuli — in the mice that weren't able to run. These genes were turned on by the firing neurons. The brains of mice that engaged in physical activity showed an ability to control its reaction with its inhibitory neurons. These mice also showed a higher release of the neurotransmitter GABA — gamma-aminobutyric acid — which suppresses neural excitement, as well as higher amounts of proteins associated with GABA.

But to see if the response to anxiety was really reduced by GABA, the researchers administered the chemical bicuculine, which blocks GABA receptors. Indeed, they saw the anxiety-reducing effect canceled out.

The results of this study show that the brain can be adaptive in tailoring how it works based on an organism's lifestyle, the researchers said. They say that animals with a less active lifestyle may need to be anxious more often, as it will help them survive if they encounter a dangerous situation.

"Understanding how the brain regulates anxious behavior gives us potential clues about helping people with anxiety disorders." Elizabeth Gould, Princeton's Dorman T. Warren professor of psychology, said in a press release. "It also tells us something about how the brain modifies itself to respond optimally to its own environment."

Source: Schoenfeld TJ, Rada P, Gould E, et al. Physical Exercise Prevents Stress-Induced Activation of Granule Neurons and Enhances Local Inhibitory Mechanisms in the Dentate Gyrus. Journal of Neuroscience. 2013.

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