Physical activity reorganizes our brain so that its response to stress is reduced and anxiety is less likely to trouble us, according to Princeton scientists.
For the experiments, one group of mice was given unlimited access to a running wheel and a second group had no running wheel. Being natural runners, mice will dash up to 2.5 miles a night when given access to a running wheel. After six weeks, the mice were exposed to cold water for a brief period in order to stress them.
The researchers saw that the brains of active and sedentary mice behaved differently almost as soon as the stress occurred. In the neurons of sedentary mice only, the cold water spurred an increase in "immediate early genes," or short-lived genes that are rapidly turned on when a neuron fires. The lack of these genes in the neurons of active mice suggested that their brain cells did not immediately leap into an excited state in response to the stressor.
Instead, the brain in a runner mouse showed every sign of controlling its reaction to an extent not observed in the brain of a sedentary mouse. There was a boost of activity in inhibitory neurons that are known to keep excitable neurons in check. At the same time, neurons in these mice released more of the neurotransmitter gamma-aminobutyric acid, or GABA, which tamps down neural excitement.
These findings potentially resolve a discrepancy in past 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.
From an evolutionary standpoint, the research indicates that the brain can be extremely adaptive and tailor its own processes to an organism's lifestyle or surroundings. A higher likelihood of anxious behavior may have an adaptive advantage for less physically fit creatures. Anxiety often manifests itself in avoidant behavior and avoiding potentially dangerous situations would increase the likelihood of survival, particularly for those less capable of responding with a "fight or flight" reaction.
"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," said researcher Elizabeth Gould.
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Source: Princeton University