This article is about how exercise stimulates the production of new brain cells, also known as neurogenesis.
About 700 neurons are generated every day but that decrease as we age. Stress can hamper neurogenesis by the production of endogenous steroids. Lack of new brain cells can present as anxiety, depression, and later as neurodegenerative diseases like Alzheimer’s, Parkinson’s, and Huntington’s disease.
Neurogenesis occurs in the subgranular zone (SGZ) of the dentate gyrus (DG) of the hippocampus and the subventricular zone (SVZ).
The hippocampus has an essential role in learning, memory, and spatial memory. Spatial memory is what the brain needs for navigation if the GPS or Google Maps are not working.
The SVZ is very special. It is the source of new nerve cells for the whole brain. The new neurons that come from the SVZ travel down to the olfactory nerve and is responsible for the smell. However, in the event of brain injuries like radiation, chemotherapy, ischemia (loss of blood supply as in a stroke), and trauma, the stem cells from the SVG can travel to the damaged area where they contribute to repair.
How Do We Know that Exercise Affects Neurogenesis?
Exercise, like running, increases neurogenesis and stimulates the stem cells and neuroplasticity in the hippocampus where the DG is located. Multiple studies were done on mice and rats that showed that exercise increases signaling proteins like the brain-derived neurotrophic factor (BDNF), macrophage migration inhibitory factor (MIF), that are needed to facilitate the
- the proliferation of stem cells,
- maturation of the new nerve cells,
- increase the efficiency of the remaining nerve cells thru change (neuroplasticity),
- Promotes better communication between the brain cells
An example of a study done over some time is as follows. The investigators tested the rodents for anxiety and depression. (Yes, they have psychological tests for rodents). Then they made the rodents run voluntarily. It has to be stress-free. Remember that stress releases endogenous steroids that prevent neurogenesis.
The animals were tested again after running, and their symptoms of anxiety and depression significantly improved. Some of the improved animals were then sacrificed, and their brains examined for the neurokines (brain signaling proteins) and new nerve cells. The exercised rodents with improved symptoms had a more significant amount of neurokines like BDNF and new brain cells, which correlated with the improvement in their depression and anxiety.
The animals that did not exercise who of course did not have any improvement in their anxiety and depression did not have a significant increase in their brain cells
The conclusion is that one of the explanations for the advancement of symptoms appears to be related to the development of neurogenesis in the dentate gyrus and the hippocampus.
Relation Between Neurogenesis and Depression Improvement in Humans
In one study, patients with depression that are being treated with antidepressants had an MRI of the brain. What they found out is that the patients that had an improvement in their depression showed an increase in the volume of the left hippocampus. The patients that did not respond well to the antidepressants had a smaller hippocampal volume. This also indicates that antidepressants like fluoxetine may also induce neurogenesis like exercise.
Exercises like weight lifting and High-intensity Interval training can trigger the proliferation of stem cells in our body. Running also activates platelets that induce an increase in stem cell proliferation and neuronal differentiation in the dentate gyrus.
Exercise Preserves the Hippocampus Size in Humans
In late adulthood, the human hippocampus shrinks by 1-2 percent a year, which adds up in later years and manifests as memory problems. In a study by Erickson, Exercise training increases the size of hippocampus and improves memory, the investigators concluded that in aerobically trained individuals, there is a 2 percent boost in the size of the hippocampus in one year which reverses the age-related volume loss and they also did better memory tests.
Parting thoughts
Thanks for reading.
References:
Micheli at al. Depression and adult neurogenesis: Positive effects of the antidepressant fluoxetine and of physical exercise. Brain Res Bull. 2018 Oct;143:181-193.
Videbech, P., Ravnkilde, B., 2004. Hippocampal volume and depression: a meta-analysis of MRI studies. Am. J. Psychiatry 161, 1957–1966.
Botha M. The impact of voluntary exercise on relative telomere length in a rat model of developmental stress. BMC Res Notes. 2012 Dec 27;5:697. doi: 10.1186/1756-0500-5-697.
Erickson, K.I., Voss, M.W., Prakash, R.S., Basak, C., Szabo, A., Chaddock, L., Kim, J.S., Heo, S., Alves, H., White, S.M., et al., 2011. Exercise training increases the of the hippocampus and improves memory. Proc. Natl. Acad. Sci. U. S. A. 108, 3017–3022.
Image Credits:
Hippocampus By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 739, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3907047
Human subventricular zone. From a paper by Oscar Arias-Carrión, 2008.
Running Man Photo by Jenny Hill on Unsplash
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This information is very important to prevent seniors like me from developing mental related problems like Alzheimer’s disease or ulyanin. I understand that one problem of running exercise for an older adult is the damage to joints, etc because of the effect of impact on the joints. Is walking or swimming adequate to produce the needed stimulation for producing the brain neurogenesis you mentioned in your article. Also, my understanding is that there are 3 types of energy that our body use corresponding to 3 types of exercise, namely weightlifting, strenuous or vigorous exercise like jogging, and mild one like simple walking. How does this correspond to benefit producing neurogenesis?
Any daily physical activity is beneficial for the whole body. However, walking may be difficult for people with hip and knee pains. Swimming and rowing on an indoor rower are excellent alternatives that are not hurtful to the joints and works the whole body. It may be available at gyms or the local YMCA.