Exercise has been shown in many studies to improve brain functions, such as cognition, reaction time and coordination. The mechanism is usually ascribed to increased blood flow to the brain during exercise. But if you stop to think for a moment you’d come to the conclusion that this observation explains better brain function during the exercise, but what accounts for the long-term improvement? We know, for instance, that in muscles mitochondrial function is essential during exercise, but that only “chronic”, repeated exercise can increase the number of mitochondria so as to increase performance level. Do neurons, the “muscle” cells of the brain react to long-term exercise?

The body-brain axis

Increased numbers of muscle mitochondria are largely responsible for the increased resistance to fatigue and health benefits ascribed to exercise training. However, very little attention has been given to the likely benefits of increased brain mitochondria in this regard.

A study published in the Journal of Applied Physiology set out to fill this gap in our knowledge.. J. Mark Davis, a physiologist at the University of South Carolina, and his group, had mice run to fatigue on treadmill for  8 wks, 1 h/day, 6 days/wk at 25 m/min and a 5% incline. They measured several molecules that are associated with the biogenesis and content of mitochondria, such as PCG-1α  (a “master regulator” of mitochondrial biogenesis), and mitochondrial DNA (which is distinct from nuclear DNA and reflects the number of mitochondria in a neuron).

Twenty-four hours after the last exercise day they examined a variety of brain regions,  such as the brain stem and cerebellum, midbrain, hippocampus, hypothalamus, and frontal lobe. What they found was a bit surprising. The assumption had been that the neurons in the areas involved in motor functions, such as balance and motor control, would be the only, or primary beneficiaries of exercise. Not so. They found a marked increase in the biogenesis and number of mitochondria all over the brain. This allows the brain to work faster and more efficiently. and when you consider the areas that are affected you can appreciate the importance of exercise. For instance, the frontal lobe is involved in executive functions such as judgment and decision making. The hippocampus is the storage area of memory. The hypothalamus controls hunger and satiety, and the cerebellum and brain stem control balance.

In the aging brain, there is a progressive decline in the number of mitochondria. Exercise has been shown to improve not only memory, but also problem-solving and other cognitive functions. It stands to reason that these functions should improve in older people, as indeed several studies have demonstrated. In fact, they should improve across all age groups, just as muscle strength improves with exercise.

The 1st-2nd-century Roman poet Juvenal, in response to a question of what people should desire in life, replied: “a sound mind in a healthy body” (Mens sana in corpore sano). How perceptive, and without the benefit of modern scientific methods, just keen observation. The ancients intuitively realized what we are rediscovering today: the body affects the brain, which in turn affects the body. All actions are mutual, all functions are interdependent.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.

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