BRAIN CELLS ORGANIZE USING UNEXPECTEDLY SIMPLE PRINCIPLES

I fell off a bicycle once, and landed on my head. I wish I could say it was when I was a kid, but by that time, I was, at least ostensibly, a grown-up.

Whoever said you never forget how to ride a bike was mistaken. Anyway, I suffered a mild concussion and, although I could remember the accident just after it happened, I had no memory of it the next morning, or even today.

The connection between our brains and our minds has always fascinated humanity. Plato discussed the nature of the soul and its relationship to the body.

PLATO AND ARISTOTLE DISCUSSED MIND-BODY RELATIONSHIP

Aristotle also discussed the relationship between our minds and our body’s physical structure. The idea of a separate mind and body continued throughout the Middle Ages.

What philosophers call the “mind-brain” problem begins with Rene Descartes who proposed that mind and body are separate substances. Thomas Hobbes disagreed completely, arguing that thoughts and feelings are physical processes in our brain.

Dr. Stephanie Palmer is an associate professor at the University of Chicago. For the past two decades, she’s been researching the way the neurons in our brain organize themselves and encode information.

DR. STEPHANIE PALMER STUDIES BRAIN CELL ORGANIZATION

Professor Palmer is the senior author of a research paper that the journal Nature Physics published last week. It describes the general networking principles that govern the way our brain cells connect within one another.

The study included physicists and neuroscientists from the Universities of Chicago, Harvard and Yale. The research describes how neurons connect in a range of model organisms, and it may also explain other kinds of social networks.

“When you’re building simple models to explain biological data, you expect to get a good rough cut that fits some but not all scenarios,” Professor Palmer explained. “You don’t expect it to work as well when you dig into the minutiae, but when we did that here, it ended up explaining things in a way that was really satisfying”

BRAIN CELLS CONNECT USING SYNAPSES

Our brain cells, called neurons, connect with each other using synapses that allow them to interact and communicate. These interactions aren’t simply random, they’re dominated by a minority of more powerful connections.

Scientists call these stronger connection distributions “heavy-tailed” because of how they look on graphs. They’re the core of the network that enables us to move, think, communicate and learn.

Some researchers have suggested that organisms have their own biological patterns for neuron connectivity. Others have proposed that they arise from standard networking principles.

MODEL BASED ON PRINCIPLES FROM PSYCHOLOGIST DONALD WEBB

To gain a better understanding of how our brain cells establish connections, the team created a model based lab animal data and a principle from Canadian psychologist Donald Hebb. He showed that “neurons that fire together, wire together,” a phenomenon neuroscientists now call Hebbian dynamics.

In other words, when two neurons activate at once, they form a stronger connection. The more often this happens, the stronger their connection gets.

In all cases, the team’s model found that stronger heavy-tailed connections follow Hebbian dynamics. So, we can conclude that it’s mainly standard networking principles that organize our brain cells, and not anything unique about our biology.

CELLS TEND TO LINK BASED ON SHARED CONNECTIONS

The researchers also made another, unexpected discovery. Cells tend to link to one another based on shared connections. Scientists call this phenomenon “clustering.”

It’s a bit like if someone introduces you to their friend at a party. There’s a better chance that you and this third party will also become friends than if you met them randomly.

“These are mechanisms that everybody agrees are fundamentally going to happen in neuroscience,” according to Professor Holmes. “But we see here that if you treat the data carefully and quantitatively, it can give rise to all of these different effects in clustering and distributions, and then you see those things across all of these different organisms.”

PRINCIPLES NOT AS TRIM AND ELEGANT AS THEY MIGHT SEEMS

These networking principles are a huge step forward for resolving the mind-brain problem, but they’re not as trim and elegant as they might seem. Those stronger connections may work in ways that would gratify Donald Webb, but the process can also be chaotic in other ways.

Brain cells can disconnect and rewire themselves. Weaker connections often get weeded out.

Scientists call this chaotic aspect of the process “noise,” but despite the term they use, it’s vital to the process. In fact, the researchers had to refine their model to take these random variations into account.

“WITHOUT NOISE, MODEL WOULD FAIL”

As Professor Palmer’s colleague on the project, Dr. Christopher Lynn of Yale puts it, “Without that noise aspect, the model would fail. It wouldn’t produce anything that worked, which was surprising to us. It turns out you actually need to balance the Hebbian snowball effect with the randomness to get everything to look like real brains.”

The mind-brain problem seems to be as old as humanity itself. We clearly have a physical body, including a brain, yet somehow our thoughts and our emotions seem to create some sort of separate experience.

AND ANOTHER THING…

Humanity needs a better understanding of the peculiar, self-organizing property our brains seem to have. It’s another part of the new story we’re all seeking to comprehend who we are, and our place in the world.

The scientists are fascinated by the idea that these networking principles probably explain other phenomena. This could lead to discoveries far beyond how our brains work.

Professor Palmer concluded by saying, “The folks on this team have a huge diversity of knowledge, from theoretical physics and big data analysis to biochemical and evolutionary networks. We were focused on the brain here, but now we can talk about other types of networks in future work.”

We always have more to learn if we dare to know.

Learn more:

Surprisingly simple model explains how brain cells organize and connect

Heavy-tailed neuronal connectivity arises from Hebbian self-organization

Brain Cells Have Mysterious Self-Organizing Ability

Dying Brains May Experience Surge of Consciousness

Brain Scans Enable Scientists to Read Minds