Does Your Brain Get Tired Like the Rest of Your Body?

So let's get this out of the way first. Your brain is technically an organ, not a muscle. It does have a bit of muscle tissue, but for the most part it's mostly fat. In the brain, electrical cells called neurons transmit messages via chemicals. Although the brain isn't a muscle, its cells do use energy to function.

"The brain requires fuel and energy," says Gary Figiel, M.D., a geriatric psychiatrist in Atlanta who specializes in neurology and psychiatry. "The brain uses glucose as the primary source of energy." When glucose enters the brain's cells, it gets turned into adenosine triphosphate (ATP), a complex organic chemical for storing and transferring energy in cells, by the mitochondria.

It's the compound ATP that researchers from Australia and Belgium thought could be the key to brain drain. The idea was that when your brain works hard, it uses up all that glucose, leaving you feeling depleted. The lowered glucose levels then raise levels of ATP, which blocks dopamine — that chemical that makes you feel good and keeps you motivated.

The study, which was published in the journal Sports Medicine in 2018, concluded that when your brain can't get enough dopamine, you're less likely to stay on task. So even though your brain is not a muscle, chemically you can tire it out by thinking too much.

"We are not wired to use the 'higher order executive function' all the time," says Melanie Greenberg, Ph.D., clinical psychologist in the Bay Area, California, and author of "The Stress Proof Brain." While "higher order executive function" can include obvious tasks like taking the LSAT, it can also comprise a combination of smaller challenges, like processing a lot of new information coming at you at once.

"After a while, our brains automate things and take less energy," Greenberg says. For example, if you drive the same way to work every day, that activity will use less brain energy than if you had to constantly find new routes. When your brain is dealing with an ongoing supply of new information, it must put energy into every decision, which overuses that executive function and can cause mental fatigue.

Although using up available glucose in your brain creates mental fatigue, simply taking in more glucose won't fully and immediately recharge your brain. Eating a snack or having coffee can help, but neither will eliminate the brain drain because the cellular functions are more complicated than that.

Every brain cell is connected to 100,000 other cells in a highly integrated network, and when you're tired, your brain has decreased blood flow and electrical activity, Figiel explains. Scientists are still in a hypothetical stage of understanding the brain. They know that rest is important, however they still aren't sure why it's important to our brains.

But simply put, there are four steps to a well-functioning brain, Figiel says:

A breakdown in any of the four steps could be to blame for mental fatigue, Figiel says. If glucose is available, a cellular function could slow down or work improperly. However, the technology available to scientists today does not provide cellular-level information. These are questions currently being researched.

Whether scientists can explain it or not, mental fatigue feels real when you have it. When mental challenges — whether it's work, today's political climate or just the fast pace of modern life — are constantly coming at you, your stress response can keep getting switched on. These can prompt your body to release a lot of the stress hormone cortisol.

"Stressors are not meant to be on all the time," Greenberg says, and they are what also lead to "burnout," which she describes as "dealing with so many problems or things that don't have solutions." This kind of mental and emotional fatigue from overstress can affect your immune system and interfere with concentration, memory and focus.

The good news is you can avoid mental burnout. Just knowing that there are limits to your brain function — glucose or not — will help you think differently. The prefrontal cortex, where your higher-order thinking is done, takes a lot of energy, so your brain cannot perform complex tasks all day. So consider completing your most challenging activities in the morning.

"Some of it is living a more balanced life if you can, try not to take on too much, have boundaries," Greenberg suggests. When considering new responsibilities, look at the pros and cons. "Have a regular stress management routine that can rest your brain or give you energy. It has to be regular."

But if you're experiencing mental fatigue and don't have a clear cause for why — like a particularly hard day at the office or a tough French exam — Figiel recommends checking for a medical issue. Because people are affected differently cognitively, just as they are physically, changes in your usual cognitive emotions should raise a red flag.

Keeping a healthy diet and lifestyle helps here too — getting enough sleep, not being too hard on yourself and not being a perfectionist.

"If you are experiencing a kind of burnout, you should try to figure out what the cause is," Greenberg says. Your brain can only do so much. Until science finds out more about the innerworkings of brain cells to help them do more, you'll have to focus on lifestyle changes.

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