Why is exercise such an important part of our lives? Does it really have more than the physical benefits? The answer, of course, is yes! Physical exercise is not only good for our bodies, but it also helps to improve our mental health. It is widely known that regular exercise helps control stress-related disorders such as depression and anxiety. So, why is this the case? Nishii et al. (2017) found that four important events are involved in making us feel better in response to exercise.
The first three events can be thought of as a baseball game. The dorsal raphe nucleus (DRN), an area in the brain, is filled with serotonin receptors. Serotonin is an important substance in our nervous system that regulates our mood, but in this case, can be thought of as the baseball. The serotonin receptors are like little catchers in our brain; catching the serotonin when needed. When the baseballs are caught by the catchers, the game is won and our mood is elevated.
We could think of our stress response system called the hypothalamic-pituitary-adrenal axis (HPA) and a part of our brain called the hypothalamic paraventricular nucleus (PVN) as the opposite baseball team, working together as team players. In response to stress, the PVN releases a hormone called corticotrophin that activates the HPA axis (the PVN throws the hormone baseball and the HPA catches it). These baseball players activate our response to stress.
Lastly, a structure in the brain called the hippocampus, responsible mainly for memory, must do its part.There has been evidence that part of the reason that exercise fights stress is because of the growth of new cells in this area.
The experiment that Nishii et al. (2017) performed involved using rats to examine what actually happens in these important areas after exercising. The rats were first trained on how to run on a treadmill for 10 days and then split into three groups (one group being the control group, which means these rats just sat on a treadmill without moving). The first group then ran on a treadmill for 30 minutes, some of them at a low speed and some at a high speed. They were then put in a deep sleep and had their brains removed to be examined. The researchers found that activity in the DRN increased more in the rats running at low speeds than the rats running at high speeds. In other words, the baseball players inside the low-speed running rats were playing much better than the baseball players of the high-speed running rats in this area of the brain. You may ask yourself, if exercise really does reduce stress-related symptoms, shouldn’t the rats who were more physically active play the better game? Researchers suggested that treadmill running at high speeds may have actually caused stress in the rats, as they only had one chance to try it at this intensity. This was further backed up by the increase in performance by the opposing baseball team (the PVN and HPA), with the high-speed running baseball team playing much better, increasing the stress response in the rats. The absense of growth in the hippocampus suggested the same thing.
The second group continued these daily running sessions for four weeks, and then performed a test called the Forced Swim Test, in which they were placed in a small swimming pool and examined for how much they moved around. The more the rats moved in the water, the less depressive symptoms they were said to have. After this test, the second group of rats had their brains examined. The rat’s brains were tested for a hormone that indicated activity in the cells of the DRN and PVN and a protein that indicated cell growth in the hippocampus. The researchers found lots of activity in the DRN in both the high-speed running rats and low-speed running rats. It was also found that activity in the PVN, leading to the activation of the HPA, was reduced in this group, regardless of the speed. Lastly, the density of the hippocampi in this group of rats were all larger than before the rats started running! So, why did things go so well for this group? It turns out that, since these rats were exposed to treadmill running daily for four weeks, the activity stressed them out less, increasing the sensitivity of the DRN cells, decreasing the sensitivity of the PVN cells, and causing the hippocampus to grow. In other words, with regular exercise, the baseball players in the DRN got adequate practice and were able to beat the PVN and HPA team. These results were consistent with the behavioral test, as the active rats moved more in the swimming pool than the control rats.
These results mean that exercising regularly can in fact reduce stress-related symptoms and it is caused by the four important events stated by Nishii et al. (2017). So, the next time you are playing baseball for physical exercise, think of the tiny players inside of you cheering you on.
References
Nishii, A., Amemiya, S., Kubota, N., Nishijima, T., & Kita, I. (2017). Adaptive changes in the sensitivity of the dorsal raphe and hypothalamic paraventricular nuclei to acute exercise, and hippocampal neurogenesis may contribute to the antidepressant effect of regular treadmill running in rats. Frontiers In Behavioral Neuroscience, 11doi:10.3389/fnbeh.2017.00235
