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Experts say multi-tasking is one way to tire out your brain. 10’000 Hours/Getty Images
  • Researchers have discovered a possible mechanism to explain why our brains become fatigued.
  • When you’re feeling cognitive fatigue, it can be harder to make good choices.
  • Being aware of what causes your cognitive fatigue can help you to work around it.

It was a long day at work. You get home and toss your keys on the counter.

And then you remember: dinner.

You were going to try that new recipe, but that means peeling, chopping, and sautéing. Measuring, mixing, and timing. And then there’s the cleanup afterward.

It’s just too much. You put on your sweats and order takeout instead.

Now, there’s nothing inherently wrong with the occasional takeout meal. No, the villain in this story is cognitive fatigue.

You’ve surely felt cognitive fatigue before and probably on a somewhat regular basis.

It’s a general feeling of tiredness. Not a sleepy kind of tiredness but a mental exhaustion.

New research published today in the journal Current Biology details a possible mechanism in the brain that explains why we feel cognitive fatigue in the first place.

What causes cognitive fatigue and is there anything you can do about it?

Before we retake control of our brains, we have to talk about glutamate.

Glutamate is a metabolite, which just means it’s something your body makes when it converts food into energy.

But it’s not just any metabolite. It’s also the most abundant neurotransmitter in your brain.

This means it’s an important chemical messenger that allows your brain cells to communicate with each other.

So far glutamate sounds pretty great. Of course, you’ve heard of having too much of a good thing, right?

Researchers in Paris wanted to better understand the mechanisms behind cognitive fatigue, so they did some digging.

In their study, participants were given a series of tasks to complete and then asked to make various economic choices.

The researchers then looked at the metabolites in participants’ brains using magnetic resonance spectroscopy (MRS), a type of medical imaging scan.

The results revealed that work that was more cognitively demanding led to a buildup of glutamate in the lateral prefrontal cortex (LPFC).

Experts believe this part of the brain plays an important role in several tasks, including:

  • inhibition
  • paying attention
  • planning
  • problem-solving
  • working memory

The researchers say that once this accumulation of glutamate occurs, it might require extra energy to activate your LPFC.

In other words, after you’ve made a lot of choices — especially tough choices that take a lot of brain power — you might be more inclined to “press the easy button.”

While this new neuro-metabolic theory of cognitive fatigue is interesting in its own right, the question remains: What can you do about it?

Dr. Alex Dimitriu, an expert in psychiatry and the founder of Menlo Park Psychiatry & Sleep Medicine in California and BrainfoodMD, told Healthline that first you need to take stock of what it is you’re actually feeling.

“See how you’re feeling on the weekend if you’re not working. It’s important to understand if the fatigue is due to your sleep, or your anxiety, or your actual level of busyness during the day,” he said.

While it wasn’t the study’s main focus, it does mention that glutamate concentrations decrease during sleep.

“I think it starts with sleep the night before and sleep in general. Sleep is fundamental and I think getting enough of it regularly is probably the best way to fight cognitive fatigue,” said Dimitriu.

Jennifer Bramen, PhD, a senior research scientist at the Pacific Neuroscience Institute at Providence Saint John’s Health Center in California, told Healthline that avoiding task switching (multi-tasking) can help prevent your brain from getting worn out.

“Spend blocks of time focused on a single activity,” said Bramen.

“I block off chunks of time to do desk work, then take a short (2 minute) mental break before I engage in a new task. I rest during my break instead of, for example, surfing the internet or looking at my phone. Then I switch to my next block of work,” she said.

“We often bounce between all of these multiple times in a one-hour block. That increases cognitive fatigue but not productivity,” Bramen added.

Changing your physical surroundings during your breaks might also provide benefits.

“During the day I think it’s important to take breaks and get some exercise. It’s so tempting to stay glued to your desk, but we need to get up and stretch, get some fresh air, get some sunlight,” Dimitriu said.

“Caffeine is a last and final go-to, but that helps too. Just don’t drink coffee later than noon. Having a cup of coffee and then taking a quick thirty-minute power nap can be a powerful combination,” he added.

While glutamate levels in your brain might have short-term consequences for your ability to make decisions, they impact your health in the long run, too.

“Excess glutamate is excitotoxic, meaning that over the long term it can increase neurodegeneration. Learning the skills needed to regulate your brain’s level of excitement is important for your long-term cognition,” Bramen said.

Try to take note of those times you’re feeling cognitive fatigue and set yourself up to not have to make decisions at those times.

“When you are in that state you may make even unimportant decisions poorly. In general, when you are tired you are likely to opt for things with short-term rewards and which take very little work,” said Bramen.

And what about that takeout scenario?

“If you want to set yourself up to make a healthy choice after a long day, make the choice at another time, and do work in advance. I do a lot of meal prep,” Bramen said.