A study from Princeton University has augmented the growing body of research that explains the salubrious effects of exercise. Researchers discovered that physical activity is linked to the brain’s ability to respond to stress and reduce the anxiety that would otherwise interfere with normal brain function.

This research is based on an observation of mice. Two groups of mice were used: one with access to a running wheel and one without. Mice, when presented with the opportunity, make great use of the running wheel, running up to four kilometers per night. After six weeks, both groups of mice were exposed to cold water—a stressor.

The scientists observed a marked difference in how the brains of the active and sedentary mice responded. As soon as the stressor occurred, the sedentary mice showed neural activity in “immediate early genes,” which are genes that activate when a neuron fires. However, the active mice did not display this neural activity. Furthermore, the active group exhibited activity in neurons that inhibit other, more excitable neural signals, such as those observed in the sedentary mice.

The young neurons—immediate early genes—active in the sedentary mice appear in a section of the brain called the ventral hippocampus, which is a part of the brain responsible for reducing anxiety. Researchers had long been puzzled by these excitable neurons in this part of the brain because they expected that more stress would result from their presence. The researchers at Princeton discovered that exercise, in addition to stimulating the growth of new neurons, also fortifies the mechanisms that inhibit the excitable neurons. This means that exercise simultaneously generates neurons that would cause stress and the neurons that inhibit that same stress. The inhibitory neurons persist in the brain, acting on stressful stimuli even when not exercising.

This research contributes to a body of knowledge that specifically explicates exercise’s benefits.  The study’s senior author, Elizabeth Gould, professor of psychology at Princeton explained that “Understanding how the brain regulates anxious behavior gives us potential clues about helping people with anxiety disorders. It also tells us something about how the brain modifies itself to respond optimally to its own environment.”

The research was published in the Journal of Neuroscience.

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