Scientifically Speaking | How our brains benefit from exercise

Researchers have known for years that exercise is good for the brain. Now, we know more about how it exerts its effects. This should be an incentive to get moving in the new year.

We like to think that our brains are separate from the rest of our bodies, but this isn’t true. Our brains are a part of our bodies and are shaped by movement. There is even a view among many neuroscientists that the brain evolved in more primitive animal ancestors to coordinate movement.

In fact, there are even some animals that lose their brains once they stop moving. For example, a young sea squirt will keep its brain while it is moving underwater. Once a sea squirt matures, it is fixed to rock and is no longer moving around. At that point, it digests its own brain because it is no longer required.

In early childhood, the neurons from the eye make it to a part of the brain known as the visual cortex. In fact, the brain creates its own structure and organization during a critical period of life. The brain trains itself with input from the eyes while walking, so vision during motion is seamless. Because the brain can shape itself, it is neuroplastic.

Children are born with a number of growing neurons. Scientists used to believe that adults couldn’t form new functional neurons. But that turns out not to be the case. One of the most exciting and hopeful discoveries of the past few decades is adult neurogenesis. In certain parts of the brain, neurons are generated throughout life and then become a part of existing brain circuits.

New experiences, memories, and creative activities challenge the neurons in the brain to form new connections. Neuroplasticity allows us to adapt but it also does tend to get slower with age. Maintaining an active lifestyle with exercise is neuroprotective and thought to help the brain function well for longer.

In a scientific article published on December 8 in the journal Nature, Stanford University researchers led by Tony Wyss-Coray found that laboratory mice that had been exercising had factors in their blood plasma that protected their brains from inflammation. Exercising mice also had improved brain performance compared to their sedentary counterparts. The researchers found that these results could be translated into exercise therapy for people.

The team was able to find a few dozen factors that were more abundant in the plasma of physically active mice. They also found a few factors that were scarcer. So, they examined which ones were linked to improved function and the formation of new neurons in the brain.

Brain inflammation can lead to a decline in cognition. A single protein called clusterin found in the plasma of physically active mice had an anti-inflammatory effect. This effect could be transferred to sedentary mice through transfusion. Amazingly, the brain activity and neuron-forming ability were gained even without exercise!

Clusterin has several functions in cells that line blood vessels in the brain. Some of these cells are inflamed in Alzheimer’s patients. But up until now, we didn’t know just how exercise exerted a protective effect on brains through this protein.

The authors think what happens is that clusterin and other exercise factors are produced by the liver after exercise. These exercise factors make their way to the brain where they exert their brain-preserving effects.

The scientists didn’t stop at mice studies, however. They recruited elderly people with mild cognitive impairment to see if these results applied to humans. They do. Six months of aerobic exercise increased clusterin levels in human blood plasma too.

These results are important because those with mild cognitive impairment are at a greater risk of progressing to dementia than the general population. Many cognitive declines have been attributed to a part of the brain known as the hippocampus. Fortunately, the hippocampus is a part of the brain where we can continue to grow new neurons through life. The adult hippocampus grows around 700 new neurons per day, and this can be promoted by exercise.

There are many known health benefits to aerobic exercise. What has often been lacking is a biological understanding of just how exercise exerts these positive effects. With this study, we now know that the production of exercise factors (like clusterin) in the blood leads to reduced inflammation in the brain, improvement of memory, and growth of new neurons.

It may be that these results will one day lead to pills that give people the mental benefits of exercising. But that’s hardly necessary for most of us. We just need to put on some running shoes and hit the road. Our brains were designed for it.

Anirban Mahapatra, a scientist by training, is the author of COVID-19: Separating Fact From Fiction 

The views expressed are personal

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