Effects of Exercise on Memory

 Research has shown that physical exercise is highly beneficial to people’s physical and mental health. Indeed, many doctors claim that if exercise could be offered as a pill, it would be the most frequently prescribed one because exercise has so many benefits (Butler, 1978). Physical exercise includes activities that raise people’s heart rate and physically works the body, including playing sports and lifting weights. Exercise can make people happier and lower levels of depression and anxiety. Also, exercise helps to prevent disease, slows down aging and the onset of Alzheimer’s disease, which leads to memory loss. While there is strong evidence that exercise improves hippocampal memory in rodents, there are some mixed evidence about how well exercise improves hippocampal memory in humans. Overall, exercise improves hippocampal memory in humans and can slow down cognitive decline in older adults.

Exercise has been shown to increase BDNF (brain derived neurotropic factor) levels in the hippocampus of rodents (Neeper et al., 1995). Rodents that exercise longer on hamster wheels have higher levels of BDNF. BDNF contributes to neurogenesis, or the creation of new neurons, and the growth of dendrites. BDNF protects neurons from damage and injury. Moreover, since exercise seemed to increase BDNF activity the most in highly plastic areas of the brain, exercise seems to be involved in brain plasticity and changing the brain structure. Also, exercising may help reduce age-related cognitive decline and Alzheimer’s disease because BDNF activity is greater in forebrain cholinergic neurons, which are associated with these functions (Neeper et al., 1995). Moreover, exercise activates the same genes that are needed for learning and memory such as BDNF and CREB (Berchtold, Chinn, Chou, Kesslak, & Cotman, 2005).

Young adults with higher baseline levels of fitness, as measured by their oxygen consumption levels of Vo2max, had larger hippocampal volume as measured by MRI and greater neural elasticity as measured by MRE. Those with greater aerobic fitness also performed better on a spatial memory task. In young adults, aerobic fitness changes hippocampal structure and improves hippocampal viscoelasticity, which is associated with greater associative memory (Schwarb et al., 2017). However, since this study is correlational, we cannot know for sure whether exercise has a causal relationship with better associative memory.

In another study, young adults participated in one 30-minute session of high-intensity exercise, low-intensity exercise, or relaxation (Hotting, Schickert, Kaiser, Roder, & Kassow, 2016). Researchers found that participants who participated in the high-intensity exercise group showed greater memory consolidation because, although they were recalled less words on a word recall task, they forgot less of the words compared to the low-intensity and relaxation groups. Researchers did not find a relationship between peripheral serum BDNF levels and performance on the memory task. However, one limitation of the study is that, due to ethical concerns, the researchers could not measure BDNF levels in the brain, so the peripheral BDNF levels may not reflect the true BDNF levels (Hotting et al., 2016).

 Participants who were assigned to run three times a week for thirty minutes each for six weeks had greater positive mood and greater visuospatial memory, as measured by a test involving retracing map directions. compared to the control group, which did not change its regular exercise levels (Stroth, Hille, Spitzer, & Reinhardt, 2008). However, exercise did not improve verbal memory and concentration abilities. Although one potential limitation of the study is that participants were aware of which experimental group they were in, potentially exaggerating the effects due to participant bias. Yet since this study was experimental and was not affected by selection bias, it provides strong evidence that exercise improves visuospatial memory (Stroth, Hille, Spitzer, & Reinhardt, 2008).

Older adults may acquire different effects from exercise than younger adults because older adults’ brains are experiencing cognitive decline (Schwarb et al., 2017). The hippocampus decreases in volume by around 1-2% annually in older adults (Erickson et al., 2011). In a study by Erickson et al. (2011), researchers investigated whether long term exercise can improve memory in older adults. In the experiment, 120 older adults took a baseline fitness assessment measuring MRI and fitness and memory levels and were randomly assigned to an aerobic exercise group and a stretching control group. In the aerobic exercise group, participants went on three 40-minute walks per week for six months and one year. Compared to the stretching control group, the participants in the aerobic exercise group showed an increase in volume of the anterior hippocampus, which helped them on a spatial memory task involving remembering the location of dots. Moreover, hippocampal volume increased by around 2%, which prevented the usual annual decrease. Thus, exercise can improve spatial memory in older adults.

Although exercise improved memory of rodents, the evidence is not as conclusive in humans (Voss et al., 2019). Also, a National Academics report reports that there is not enough conclusive evidence to recommend exercise in preventing age-related cognitive decline and dementia (Downey et al. 2017). In its meta-analysis of multiple studies, there were inconsistent results on cognitive benefits (Downey et al. 2017).

However, some of these studies challenging the benefits of exercise used different experimental methods. For instance, a one-year study is unable to fully appreciate the effects of exercise on preventing dementia. Also, these studies did not measure cardiorespiratory fitness (Voss et al., 2019).

There is much evidence that exercise improves memory. Aerobic exercise increases brain volume and hippocampal size in aging humans (Colcombe et al., 2006; Erickson et al., 2011). Exercise improves cognitive abilities in both children and older adults (Hillman, Erickson, & Kremer, 2008).

Discussion, future studies. More long-term studies measuring BDNF and exercise would be helpful.

Conclusion: Considering all this evidence, although we cannot be conclusive, there is stronger evidence supporting exercise’s role in enhancing memory, thinking, and brain size.

References

• Colcombe, S. J., Erickson, K. I., Scalf, P. E., Kim, J. S., Prakash, R., McAuley, E., … & Kramer, A. F. (2006). Aerobic exercise training increases brain volume in aging humans. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 61(11), 1166-1170.
• Downey, A. et al., eds (2017). Preventing cognitive decline and dementia: A way forward. National Academies Press.
• Erickson, K. I., Voss, M. W., Prakash, R. S., Basak, C., Szabo, A., Chaddock, L., … & Wojcicki, T. R. (2011). Exercise training increases size of hippocampus and improves memory. Proceedings of the National Academy of Sciences, 108(7), 3017-3022.
• Hillman, C. H., Erickson, K. I., & Kramer, A. F. (2008). Be smart, exercise your heart: exercise effects on brain and cognition. Nature reviews neuroscience, 9(1), 58.
• Voss, M. W., Soto, C., Yoo, S., Sodoma, M., Vivar, C., & van Praag, H. (2019). Exercise and Hippocampal Memory Systems. Trends in cognitive sciences.
• Butler, R. N. (1978). Public Interest Report No. 23: Exercise, the Neglected Therapy. The International Journal of Aging and Human Development, 8(2), 193-195. 
• Berchtold, N.C., Chinn, G., Chou, M., Kesslak, J.P., & Cotman, C. (2005). Exercise primes a molecular memory for brain-derived neurotrophic factor protein induction in the rat hippocampus. Neuroscience, 133, 853-861.
• Hötting, K., Schickert, N., Kaiser, J., Röder, B., & Schmidt-Kassow, M. (2016). The effects of acute physical exercise on memory, peripheral BDNF, and cortisol in young adults. Neural Plasticity, 2016.
• Schwarb, H., Johnson, C. L., Daugherty, A. M., Hillman, C. H., Kramer, A. F., Cohen, N. J., & Barbey, A. K. (2017). Aerobic fitness, hippocampal viscoelasticity, and relational memory performance. Neuroimage, 153, 179-188.
• Stroth, S., Hille, K., Spitzer, M., & Reinhardt, R. (2009). Aerobic endurance exercise benefits memory and affect in young adults. Neuropsychological Rehabilitation, 19(2), 223-243.