The Beautiful Logic of Brains on the Brink
Let’s start with a strange but serious question:
How does the brain stay stable without getting stuck?
It’s a biological paradox. Your brain is always changing—learning, forgetting, adapting—yet somehow never spins out of control. It doesn’t overheat, freeze up, or collapse under the weight of its own complexity. Even as billions of neurons fire off electrical signals every second, it all holds together.
Why?
Two scientists, Keith Hengen and Woodrow Shew, think they’ve found the answer. In a sweeping new paper, they argue that the brain keeps itself balanced by operating near something called criticality. It’s a mouthful, but the idea is surprisingly intuitive: the brain, at its best, runs near a tipping point between chaos and order. Not too rigid. Not too random. Just close enough to the edge to stay flexible, but not fall off.
Think of it like surfing. Too far from the wave, and you don’t go anywhere. Too far forward, and you wipe out. But if you ride right at the edge? You get the power, the speed, the control. That edge, they argue, is where the brain likes to live.
The Brain’s Balancing Act
Every part of the brain is built to adjust—constantly. That’s how we learn new things, recover from setbacks, and adapt to surprises. But there’s a catch: too much change, and the system becomes unstable. Imagine a thermostat that keeps turning itself up and down with no middle point; it either overheats or freezes the house.
The brain avoids this by finding a set point: a place where all the moving parts balance out. Hengen and Shew think that set point is criticality—a kind of “sweet spot” where the brain is just sensitive enough to detect important changes, but not so sensitive that it overreacts to every little thing.
At this sweet spot, the brain can store information, send signals efficiently, and even make new patterns on its own. That’s a big deal. Because it means the brain doesn’t just respond to the world—it can imagine new possibilities.
The Hidden Pattern Behind the Noise
For years, scientists have argued about whether the brain really operates at this so-called edge. Some found hints of it. Others didn’t. The data were confusing. It looked like everyone was measuring the same thing—and coming up with different answers.
But Hengen and Shew noticed something simple: the way people looked at the data changed what they saw. Specifically, it came down to how researchers divided time into chunks. If you sliced the brain’s activity into very short time windows, you’d miss the bigger patterns—like trying to understand a song by looking at single notes. But if you zoomed out a bit, the structure became clear.
Their re-analysis of 140 studies showed that when you look at brain activity with the right lens, signs of criticality show up across animals, experiments, and techniques. It’s not random. It’s universal.
Curious? Conflicted? Caught off guard? Say something true, and let’s think out loud together.
A Brain That Comes Back to Itself
What’s even more compelling is what happens when the brain gets knocked off balance. After surgery, after sensory deprivation, even after certain types of anesthesia—the brain tends to drift back toward criticality. It’s not just a temporary state but a kind of home base.
This helps explain why disruptions to criticality often show up in brain disorders. In epilepsy, the brain becomes too synchronized—locked into repetitive storms of activity. In depression, autism, and schizophrenia, the opposite may happen—patterns break down, connections weaken, and the brain becomes too disorganized to function properly.
(For more on what happens when the brain can’t adapt—when its belief-updating system seizes up instead of staying fluid—see The Bayesian Mind, where I explore a complementary theory of mental health through the lens of probabilistic reasoning.)
In either case, the system has drifted away from the edge. And with it, the flexibility that makes healthy thinking possible.
The Brain’s Natural Readiness
Criticality isn’t just about stability. It’s about readiness.
Machine learning researchers know this well: if you want an algorithm to learn something new, you can’t just throw data at it. You have to start from the right place. The same may be true for the brain. If it’s not in the right mode—sensitive, balanced, open—it may not be able to learn at all.
Criticality creates that mode. It sets the stage for everything else. Before you can focus, remember, speak, or decide—your brain has to be in a state where such things are even possible.
It’s like tuning an orchestra before a concert. If the instruments aren’t in sync, it doesn’t matter how good the musicians are. The music won’t work.
Why This Matters
If Hengen and Shew are right, then criticality isn’t just a quirk of brain function. It’s the foundation. The place all good thinking begins. And understanding it could open new doors—not just in neuroscience, but in medicine, education, even artificial intelligence.
It’s a radical idea. But also a strangely comforting one.
Because if the brain really is built to stay near the edge—not in perfect balance, but in dynamic, self-correcting motion—it means we are, too. Adaptable. Resilient. Capable of returning to ourselves even after we’ve been pushed.
A little chaotic. A little ordered. And just unstable enough to grow.