Great Thinking Is Supposed to Make Your Brain Hurt

Whoever first said the brain is like a muscle was closer to the truth than they probably knew.

Spend an hour wrestling with a crossword puzzle, tackling a Sudoku grid, or calculating the area under a parabola, and you’ll feel it firsthand: Your brain is not an inexhaustible source of great thoughts and peak performance.

The brain has its limits.

One of the greatest pursuits a curious person can undertake is learning how to push those limits farther, without breaking them.

Those who’ve tried may have found that good thinking—the insightful, heavy-lifting kind—is not just hard. It can bring about sensations startlingly close to physical fatigue, even pain.

This is where the brain-as-muscle analogy comes together.

In 2022, Mathias Pessiglione and colleagues at the Paris Brain Institute published research showing that intense cognitive work doesn't simply "tire" the brain in some vague way; it physically alters the chemical environment inside it.

Their study, published in Current Biology, found that after several hours of hard mental work, participants had increased levels of glutamate (an excitatory neurotransmitter) building up in the lateral prefrontal cortex, which is the brain region responsible for higher-order thinking.

Glutamate is essential for neural communication, but too much of it can be toxic to neurons. In effect, sustained mental effort generates a kind of "metabolic residue," not unlike the lactic acid that accumulates in overworked muscles.

The brain, sensing this, sends fatigue signals to encourage you to stop before damage sets in.

Anyone who’s ever tried to work through a dense thesis at the library, or who’s had the pleasure of meeting a PhD student mid-dissertation, knows the look of this particular form of cognitive exhaustion and the havoc it can wreak all too well.

The analogy also teaches us something hopeful: Just like muscles, our brains can be trained to handle increasingly heavy lifting.

The first lesson follows intuitively. To improve cognitive performance, you need to apply progressive challenge, just like with muscles.

Lifting the same weight over and over won’t build your triceps. And thinking about the same ideas, solving the same easy problems, or rereading familiar information won’t grow your mind either.

Good thinking requires a constant gradient of challenge, new problems to solve, new concepts to wrestle with, and new patterns to map out.

Studies in cognitive aging, such as the ACTIVE trial (Ball et al., 2002), have shown that older adults who engage in ongoing, progressively challenging cognitive activities maintain sharper mental functioning longer than those who do not, at times to the point where the impact can help counteract dementia.

Another meta-analysis (Valenzuela & Sachdev, 2006) found that lifelong cognitive engagement, not just any mental activity, but mentally demanding activity, is also associated with a lower risk of dementia.

The brain, it seems, rewards those who keep it on an incline.

In a sense, good thinking should make your brain hurt.

Growth demands it. So does sustaining the gains made. Just like with muscles.

The real question is: how do you keep the challenge alive without tipping into burnout?

One answer is to explore the world broadly.

The easiest way to bore your brain is to deprive it of novelty and pattern recognition. New environments, new ideas, and new combinations of old knowledge; these all offer the cognitive equivalent of new terrain to climb.

And even if you can't physically travel, you can still explore. Read outside your specialty and engage in productive epistemological trespass.

Interleave your learning, mix disciplines, juxtapose fields, keep your intellectual metabolism guessing. Never stop being curious.

And crucially, remember Pessiglione’s findings: There are real biochemical limits to sustained thinking.

When your brain tells you it’s tired, it’s not being lazy. It’s protecting itself.

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Taking breaks, going for long walks, or even zoning out in front of a favorite Netflix show aren’t acts of intellectual abdication. They’re active recovery. They’re what allow you to return to the grind tomorrow, a little sharper and a little stronger.

The brain is a marvel of endurance, but it’s not limitless. Stretch it, challenge it, push it to think harder and deeper. But also let it breathe. Because in the end, the goal isn't just to think more or for longer. It's to think better.

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