Role of Exercise and Stress in Memory and Learning of the Hippocampus
Dr. Jeff Edwards, Neuroscience
Some of the most devastating diseases today are diseases of the mind. Common side effects of Alzheimer’s disease are dementia and memory loss and more than 44 million people suffer from the disease worldwide . Other mental diseases such as Parkinson’s also have a dramatic impact on the memory and learning pathways. Understanding the mechanism involved with memory and learning will bring science that much closer to finding a permanent cure to these devastating diseases.
The brain is the last frontier of medical and scientific research. Overly complex, and extraordinarily difficult to study, cerebral research is the focus of some of the world’s greatest minds. On the forefront of that research is our ability to form and store memory. Memory plays an essential role in every aspect of human life, but can be greatly diminished as stress levels increase. Determining what role exercise could have in mitigating the negative results of stress could be instrumental in decreasing health related memory impairments or other stress induced abnormalities through exercise therapeutics.
The purpose of my project was to study the relationship that Exercise and Stress have on the formation of memory and learning. One of the major functions of the hippocampus of the brain is to mediate strength or weakness of memory formation and continued learning. When an individual undergoes increased memory formation, a process called Long-Term Potentiation (LTP) is initiated and increased memory formation occurs . It has previously been proven that elevated levels of stress will adversely affect the formation of memory, whereas, exercise will increase LTP and memory formation . No research has previously been performed where subjects have been under both the influences of stress and exercise. My research addressed that issue. I tested whether the positive benefits of exercise could overcome the negative consequences of stress in memory formation.
In my project, I used mice to test the effects of stress and exercise on memory. For my experiment, I grouped my mice into four different groups; exercise without stress, sedentary without stress (control group), exercise with stress, and sedentary with stress. To quantify the mitigating effects of exercise on stress, I used the Radial Arm Maze (RAM). The RAM is a simple structure that has an open middle space with 8 arms or passages extending equidistant to the center that the mice can travel down. I placed cheese strategically in a combination of the different arms. The same arms were baited identically in each trial to eliminate potential error. The mice were timed to see how long it took them to find all of the cheese and the number of times they entered an incorrect arm was recorded.
Each mouse was tested five times a day, five days a week, for six weeks in order to test spatial, working, and long-term memory. Mice were fasted before test days in order to assure they had the proper motivation in finding the cheese and completing the maze. The mice in the stress categories were placed either in a restraining tube or on a high stand immediately previous to experiments to induce a stress reaction. In each experiment, we will video each trial to quantify mistakes made going down non baited arms, returning to arms previously visited, total time elapsed, and total distance covered.
Previous experiments have confirmed that the physiological brain process of LTP, or memory enhancement, is reduced in the presence of stress and increased with exercise. As expected, our results concurred with previous data. Mice in the exercise no stress category initially surpassed memory formation compared to all other categories. They made fewer mistakes and completed the maze faster. Mice in the sedentary and stress category initially did the poorest. Both the control group (sedentary no stress) and the exercise with stress were in between the other two groups, suggesting that exercise was able to mitigate the negative consequences of stress.
As the weeks proceeded, there was a plateauing effect that all groups went through. Because I continued to test the different groups of mice until they were successful in completing the maze with very few mistakes, eventually all the groups were able to successfully complete the maze. However, the time it took the exercise, stress group to memorize the maze was more similar to the control group than the sedentary, no stress group. This suggests that exercise was able to mitigate the negative side effects that stress has on memory formation.
Though our results do suggest that exercise is beneficial in reducing the negative side effects of stress, the results were not as clear as we wanted. Overtime, it appeared that the effects of stress decreased significantly. This may be due to the stress mice acclimatizing to the stressors. Some mice appeared to have little or no response to the stress. A future study could measure stress molecules in the blood or brain to help quantify how much stress each mouse has. This might better explain why certain mice responded the way that they did.
Shortcomings in the research process aside, our research is some of the first quantifiable research that suggests that the negative consequences of stress in memory formation can be reduced or eliminated by exercise. Exercise is known to have a plethora of positive health outcomes and the research can now link it to a reduction of stress events in memory formation in the hippocampus of the brain.
Alzheimer and Parkinson ’s Disease, along with many other mental disorders, greatly impact learning and memory formation in the brain. In many cases, both learning and memory are completely compromised. Many researchers and physicians are searching for a solution. Unfortunately, the learning and memory pathways are extremely complex and there is not a simple solution.
Learning and memory are essential for everyday life and my research was directed towards finding a way to eliminate the negative aspects of stress of stress on learning and memory formation. Through my research on mice, I found that exercise was sufficient to negate the negative side effects to learning and memory formation of stress.
1. “Alzheimer’s Statistics.” Alzheimers.net. N.p., n.d. Web. 29 Oct. 2015. 2. Bennion, Douglas, et al. “Transient receptor potential vanilloid 1 agonists modulate hippocampal CA1 LTP via the GABAergic system.”Neuropharmacology 61.4 (2011): 730-738. 3. O’Callaghan, Rachel M., Robert Ohle, and Aine M. Kelly. “The effects of forced exercise on hippocampal plasticity in the rat: A comparison of LTP, spatial-and non-spatial learning.” Behavioural brain research 176.2 (2007): 362-366.