Why Thinking Hard is So Exhausting

Prolonged intense thinking floods your brain with a toxic substance that acts like a circuit breaker for your mind

Robert Roy Britt
4 min readAug 11, 2022

Image: Pexels/ Andrea Piacquadio

You might want to think long and hard about thinking long and hard about things. It can leave you exhausted mentally and physically. But why, exactly? One idea — a rather flimsy one, it seems —is that the brain fabricates a feeling of fatigue to encourage us to shift from thinking hard to doing something more gratifying.

But new research suggests a more concrete mechanism is at work, and that such fatigue is your brain’s way of crying out for a serious break.

Several hours of intense thinking generates a buildup of a toxic chemical messenger in the prefrontal cortex, the brain area responsible for, among other vital functions, making decisions and solving problems, scientists explain today in the journal Current Biology. The buildup can alter how effectively we think, and it apparently pushes us to stop thinking so much, to protect the mind from overwork.

Think of it as a circuit breaker that prevents an electronic device from exploding when it overheats.

“Our findings show that cognitive work results in a true functional alteration — accumulation of noxious substances,” says study team member Mathias Pessiglione, PhD, a biologist and psychologist at Pitié-Salpêtrière University in Paris. “So fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning.”

Let’s not overthink this. It’s probably why an unrelated study I wrote about last year reached this conclusion regarding longer-term burnout:

Taking time off work to relax and rejuvenate — the defiant act of being utterly unproductive — is vital to mental well-being, to happiness.

It also supports my contention that doing absolutely nothing—literally sitting and not even trying to think about things—is great for the mind, body and soul, a concept dozens of Medium readers agree with, as you can see in the comments to this recent article:

Robert Roy Britt

Founder/editor of Wise & Well on Medium & the Writer's Guide at writersguide.substack.com & author of Make Sleep Your Superpower amazon.com/dp/B0BJBYFQCB