Exercise & Neurogenesis: The Effects of Running on Memory

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Newly born neurons in Sedentary animal [top panel] and an animal that performed voluntary running [lower panel]

By Caleb Vierkant

Newly born neurons in Sedentary animal [top panel] and an animal that performed voluntary running [lower panel]

Newly born neurons in Sedentary animal [top panel] and an animal that performed voluntary running [lower panel]

Exercise is good for you: it keeps you fit, helps avoid health problems later in life, and helps increase reflexes. It is widely believed that exercise is good for your brain as well. It boosts mood, helps learning abilities, and makes memory stronger. It even increases the rate of neurogenesis.

Neurogenesis is a process of production of new neurons from neural stem cells in the brain, according to Dr. Ashok K. Shetty, associate director and professor at the Institute for Regenerative Medicine, Texas A&M College of Medicine. “After birth, neurogenesis in most regions of the brain stops, but in two regions it [prominently] continues. One is the hippocampus, the region for learning and memory.”

Dr. Shetty adds that in one estimate, 700 new neurons are born every day in the human hippocampus.

Dr. Shetty received his Master of Science degree in anatomy in 1983 from Kasturba Medical College of Mysore University. He earned his Ph.D. in neuroscience in 1990 from the All India Institute of Medical Sciences. After some post-doctoral work, Dr. Shetty successively served as assistant, associate, and full professor at Duke University for 16 years. He came to the Texas A&M Health Science Center in 2011. He, like many other people, took the theory that exercise led to better memory as fact.

However, a 2014 study showed something unexpected. The study, using mice, revealed that more exercise, meaning an increase in neurogenesis, led to the loss of old memories. It was theorized that neurogenesis rewired memory circuits and made it harder for the mice to recall tasks they had previously learned.

photo-dr-shetty-300-dpiThis came as quite a shock to Dr. Shetty, who then decided to perform tests of his own. For their study, it was decided to use rats instead of mice.

Rats are the main model for experimentation used in Shetty’s lab. They are also physiologically closer to human beings than mice.

Rats were trained to use a water maze. This maze, a swimming pool with a hidden escape platform, tested the rats’ abilities to learn and remember. Using a series of cues to find the platform, the rodents were soon able to navigate the maze within 10 seconds.

Upon removing the hidden platform, the rats still made their way to the spot it used to be, demonstrating that the task was in their memory banks.

After this, the rats were divided into two groups. One group was given large cages to live in with running wheels. Dr. Shetty says rats love running wheels, and will use them repeatedly for voluntary exercise.

The second group was put in standard cages without running wheels.

A month later, it was time for the memory retrieval test. Both rats were taken out of their cages and put back into the water maze. Both the exercising group and the sedentary group were able to navigate the maze with equal skill. Upon examination of the exercising rats, it was discovered that in some of the rodents neurogenesis had doubled, and yet it had no effect on their memory recall ability.

“Our study very clearly shows that exercise did not interfere with memory retrieval,” says Dr. Shetty.

What does this mean for the field of neuroscience, and people in general? Dr. Shetty believes the 2014 study with the mice was an exception, rather than a rule.

“The important line is that before the 2014 study we already knew that exercise was good for you, not only physical but also in brain function,” he says. “This was already well known. Our study in rats showed that despite the [considerable] increase in neurogenesis that these rats are not losing their old memories.”

Dr. Shetty would like to see similar research performed on other species, particularly in human beings. It will be important to determine whether the correlation between neurogenesis and memory is good or bad. In the mean time, the obvious physical benefits of exercise should not be ignored, nor should the mental benefits of mood and learning ability.