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Matthew J. Edlund M.D.
Matthew J. Edlund M.D.

Is the Brain Like Muscle?

Were the jocks correct?

Grow your muscle, grow your brain. For decades it’s getting clearer—physical activity leads to more brain cells. But how? And why?

A recent paper in Cell Metabolism shows the advantages of cross-species research. Work with mice, monkeys, and humans demonstrated something jocks sensed long ago—your legs talk to your brain.

Sometimes they tell it what to do.

Catching Cathepsin B

Many of us grew up thinking the number of brain cells at birth was the most we’d ever have. Following that auspicious event, aging “wear and tear,” divorce, alcohol, and even aspirin would leave us with less and less brainpan until we emerged addled and confused onto the steps of the financially ruinous nursing home.

Except that’s rubbish.

We grow brain cells all the time. In fact, we grow new cells all the time. We completely rebuild—and quickly—the cells we have. We’re basically a continuous remake.

And now we learn that new muscles make new proteins that somehow make the brain grow new cells—and get sharper.

The study looked primarily at mice. They are a lot more manipulable than people—though observers of present-day politics might possess some doubt.

The mice given running wheels as expected showed more brain cells. They were better cognitively. They kept improving.

And they also produced a hive of proteins that popped into the bloodstream going hither and yon. One of them, cathepsin B, looked like it was directly influencing the brain (how that happens will be the subject of lots more papers, to be sure.)

So, unlike in people, mice were then bred that could not make cathepsin B. And when they were exercised, they did not get sharper. They did not make more brain cells.

In the part of the study involving people, adults who exercised got sharper. The more intensely they exercised, the sharper they got (fans of interval training might take note.)

So there was cross-species convergence. Grow new leg muscles and you make more proteins like cathepsin B. And somehow those are influencing the brain to adapt, grow, and get better at the sorts of tasks cognitive researchers really like.

Your legs have been talking to your brain all the time. Just like the jocks knew they were—even if they couldn’t fully explain it.

Muscle and Mind

So what’s going on? Perhaps we can start with three propositions to explain how bigger calves lead to bigger brains:

1. Learning is basic to life.

It’s not classroom learning we're talking about. People who study algebraic topology may receive intense pleasure and a new perspective on humans blinkered by their narrow view of a mere three-dimensional universe, but mastering algebraic topology does not automatically make you more physically healthy. Biological learning involves everything—mind and muscle, sinew and brain, ligament and lung, connective tissue and cortex. White cells learn. Red cells, too, though maybe less. Most human learning occurs below our level of consciousness. But perhaps all of it leaves residues in our brains and memories.

2. The environment changes, we change.

Environmental stimuli—whether it's bugs or bratwurst, change us. Mosquitoes bring zika virus which leaves most unaffected—many with colds, some infants with profound brain damage, and a few adults with Guillain Barre syndrome. Whatever the result, our immune systems have responded and learned from zika in ways far more profound than our political masters have. If we cannot adapt and adjust, the species disappears. We constantly learn, constantly evolve. Or we won’t be here.

3. The brain and body are information systems that learn in order to survive.

Biological information systems are complicated, multilayered, and mainly unknown. In a sea of knowledge, we possess highly fragmentary information on a few tiny archipelagoes. Despite this ignorance, we sometimes figure out quite a few things.

One is that information flows. Pretty much everywhere. Your hip bone may be connected to your thigh bone, but that bratwurst you ate last night will change the 40 trillion bacteria down in your gut in ways that may change what those bacteria communicate to the brain.

And those trillions of bacteria are communicating. Some may be messaging that they like, and want, more bratwurst. We just don’t hear that message in ways we write down.

So when you exercise and get bigger muscles, those muscles are also communicating with the brain. Because if you reshape your legs, you have to reshape your brain to handle the new stuff.

This means more memory storage and potentially greater and faster cognitive control, which means knock-on effects on the rest of the system, including your ability to read articles about exercise and the brain and draw healthy conclusions.

So the brain—and everything else—responds both to the external environment, and the changed environment of our rebuilt body. Information flows and grows. We learn and survive, and a virtuous circle is created each moment.

Bottom Line

The body is always learning. Exercise not only grows new brain cells and improves cognition but will also get you stronger, more supple muscles.

About the Author
Matthew J. Edlund M.D.

Matthew Edlund, M.D., researches rest, sleep, performance, and public health. He is the author of Healthy Without Health Insurance and The Power of Rest.

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