How Exercise Fuels the Brain

Moving the body demands a lot from the brain. Exercise activates countless neurons, which generate, receive and interpret repeated, rapid-fire messages from the nervous system, coordinating muscle contractions, vision, balance, organ function and all of the complex interactions of bodily systems that allow you to take one step, then another.
This increase in brain activity naturally increases the brain’s need for nutrients, but until recently, scientists hadn’t fully understood how neurons fuel themselves during exercise. Now a series of animal studies from Japan suggest that the exercising brain has unique methods of keeping itself fueled. What’s more, the finely honed energy balance that occurs in the brain appears to have implications not only for how well the brain functions during exercise, but also for how well our thinking and memory work the rest of the time.
For many years, scientists had believed that the brain, which is a very hungry organ, subsisted only on glucose, or blood sugar, which it absorbed from the passing bloodstream. But about 10 years ago, some neuroscientists found that specialized cells in the brain, known as astrocytes, that act as support cells for neurons actually contained small stores of glycogen, or stored carbohydrates. And glycogen, as it turns out, is critical for the health of cells throughout the brain.
In petri dishes, when neurons, which do not have energy stores of their own, are starved of blood sugar, their neighboring astrocytes undergo a complex physiological process that results in those cells’ stores of glycogen being broken down into a form easily burned by neurons. This substance is released into the space between the cells and the neurons swallow it, maintaining their energy levels.
But while scientists knew that the brain had and could access these energy stores, they had been unable to study when the brain’s stored energy was being used in actual live conditions, outside of petri dishes, because brain glycogen is metabolized or burned away very rapidly after death; it’s gone before it can be measured.
That’s where the Japanese researchers came in. They had developed a new method of using high-powered microwave irradiation to instantly freeze glycogen levels at death, so that the scientists could accurately assess just how much brain glycogen remained in the astrocytes or had recently been used.

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