How Exercise Creates New Brain Cells: The Basics of BDNF and Neurogenesis
Although the process of growing older is unavoidable, the function of your brain doesn’t have to decline with each passing year.
Scientists once thought that neurogenesis — the creation of new neurons — ceases after the first few years of life. However, research has expanded in the last few decades to verify that the creation of new brain cells extends into adulthood. The fact that adult neural cells can regenerate themselves provides exciting therapeutic options for the injured, inflamed, or diseased brain.
If you have concerns about memory loss or brain health, learn more in this article about how exercise can create new brain cells to enhance cognitive function and which type of physical activity is best for building new neurons.
What is Neurogenesis?
The previously held belief that adults cannot form new brain cells originated from the knowledge that mature neurons cannot undergo cell division, meaning that cells in the nervous system do not regenerate like other cells in the body.
However, researchers have found that adult neurogenesis does occur — not through the cellular division of mature neurons, but, instead, via the differentiation and self-renewal of neural stem cells.
Unlike pluripotent stem cells, which can differentiate into almost any cell type in the body, neural stem cells are specialized in some regions of the brain to become either neurons or glial cells, which include microglia, astrocytes, and oligodendrocytes. With their name coming from the ancient Greek word for “glue,” glial cells form the myelin that supports and protects neurons.
There are two primary areas of the brain — also known as “neurogenic niches” — in which neurogenesis occurs: the subventricular zone of the lateral ventricles and the subgranular zone of the hippocampal dentate gyrus. The hippocampus plays a crucial role in learning and short- and long-term memory consolidation.
This creation of new neurons is a subset of brain plasticity characterized by the adult brain’s ability to adapt and change its structure and rewire synaptic connections.
A brain with high levels of plasticity would be better able to repair itself after injury, leading to a reduced risk of neurodegenerative diseases and a slower aging process.
This neural plasticity allows the brain to acquire new skills, improve emotional control and memory consolidation, and continually enhance cognitive ability. One protein that plays a vital role in promoting brain plasticity and neurogenesis is BDNF.
What is BDNF?
Brain-derived neurotrophic factor (BDNF) is classified as a neurotrophin, which is a family of proteins that act as growth factors for neurons by promoting their survival, growth, and development.
BDNF is expressed in both neurogenic niches and is involved in the differentiation and maturation of neural stem cells into neurons or glial cells. Essentially, BDNF is necessary for neurogenesis to occur.
Higher levels of BDNF are linked to improved cognition and brain health in both animals and humans, while low levels of BDNF are found in individuals with neurodegenerative diseases.
BDNF is likely the mediator between exercise and improved cognitive function. A meta-analysis published in the Journal of Psychiatric Research in January 2015 analyzed the results from 29 studies looking at BDNF levels in humans after exercising. They found that both acute (single-session) and regular exercise significantly increased BDNF levels. In this study, there was a stronger association for the chronic exercisers and a reduced association for female exercisers.
The researchers indicate that each session of exercise produces a “dose” of BDNF, which can be amplified over time by creating a habitual activity routine.
In a study published in the Journal of Alzheimer's Disease in September 2013, healthy older adults and adults with Alzheimer’s disease experienced significant increases in plasma BDNF levels after just one aerobic exercise session.
In animal studies, as little as one week of exercise improved learning, memory, and cognition scores.
Exercise and Neurogenesis: Recent Research
Numerous studies have shown that exercise is linked to improved cognition. In mice, physical activity increases brain plasticity, BDNF expression, and neurogenesis, as discussed in a June 2017 review published in Neural Plasticity.
In humans, studies regarding neurogenesis are lacking because it’s difficult to measure it effectively — as of now, the only way to directly measure neurogenesis is with postmortem tissue. However, research in humans looks at hippocampal volume and BDNF expression, which may be considered proxies for neurogenesis.
Hippocampal volume tends to decrease by 1-2% per year in healthy older adults; every loss of volume is associated with an increased risk of cognitive decline.
In a randomized controlled trial published in PNAS in February 2011, older adults who were in an aerobic walking program for one year experienced a 2% increase in hippocampal volume. Not only did aerobic exercise thwart the typical age-related decline in hippocampal volume, it effectively reversed it by one to two years.
The researchers also found that those with increased hippocampal volume had greater serum levels of BDNF. Of note, aerobic exercise only increased anterior hippocampal volume, not the posterior — the anterior region is the area responsible for memory and spatial navigation.
Another potential marker of neurogenesis is cerebral blood volume (CBV), measured on MRI scans.
In a study published in PNAS in March 2007, adults underwent a 3-month aerobic exercise program. After looking at MRI scans, the researchers found that aerobic exercise increased CBV selectively in the hippocampal dentate gyrus, one of the neurogenic niches.
However, these biomarkers are not as accurate as measuring neurogenesis directly. While these results are encouraging, more research needs to be done with humans to determine the specific benefits of exercise on neurogenesis.
Does the Type of Exercise Matter?
Studies have shown that aerobic exercise is more beneficial for neurogenesis than resistance or strength training exercises.
In an animal study published in the Journal of Physiology in April 2016, rats who aerobically exercised experienced significantly greater hippocampal neurogenesis than rats who did high-intensity interval training (HIIT) or resistance training.
Even when compared to sedentary controls, resistance training did not produce any neurogenic benefits, while HIIT training did result in a small yet non-significant increase. The greatest benefits were seen in rats who performed sustained and voluntary running on a daily basis.
Another animal study found similar results. In this research, rats in the voluntary running group experienced significant increases in neurogenesis and synaptic activity in the dentate gyrus and improved scores on spatial learning and memory tests.
Aerobic exercise — especially running — boosts neurogenesis by increasing the proliferation of neural stem cells, which increases the number of stem cells that can differentiate into neurons. This cardiovascular exercise also increases the maturation of the neural stem cells into functioning brain cells. Lastly, aerobic exercise increases BDNF levels, which acts as a growth factor for neurons to develop and survive.
- Although it was previously thought that neurogenesis — the creation of new neurons — stops in early childhood, recent research has found that adults also have this ability, which can slow down the aging process and reduce the risk of neurodegenerative diseases.
- Aerobic exercise increases BDNF levels, a protein involved in neurogenesis that promotes the survival, growth, and development of neurons.
- Although neurogenesis cannot be directly studied in humans, research examining the impact of exercise on two proxies for neurogenesis — hippocampal volume and cerebral blood volume — has shown encouraging results.
- Despite ample research using laboratory animals, more studies looking at the effects of exercise on neurogenesis in humans are needed.
- The bottom line: Aerobic exercise increases BDNF and will very likely create new brain cells in as little as one activity session, with more significant benefits seen with habitual aerobic exercise.
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