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MELISSA BLOCK, HOST:

This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.

ROBERT SIEGEL, HOST:

And I'm Robert Siegel. It's easy to feel like your brain isn't very organized sometimes. But new research finds that even the most scattered mind rests on a very orderly foundation. NPR's Jon Hamilton takes a look inside our brains.

JON HAMILTON, BYLINE: The brain circuits that let us do calculus or kick a soccer ball rely on millions of tiny fibers that carry signals from one area to another. Van Wedeen of Harvard Medical School has been studying these fiber networks for years. And he says, until recently, scientific description sounded pretty chaotic.

DR. VAN WEDEEN: The model emerged that the brain looked somewhat like a plate of spaghetti or perhaps like one of those old antique telephone switchboards with a million wires running, more or less, at random between different parts of the brain.

HAMILTON: Then a few years ago, Wedeen and other researchers started looking at the brain's wiring using a new imaging technology. It showed not only the path of each fiber but all the intersections along the way. And Wedeen says that over time, his team began to see a pattern that didn't look like spaghetti at all.

WEDEEN: In the new version, pathways of the brain run in about the simplest structure you can imagine. A three-dimensional grid somewhat like Manhattan is a three-dimensional grid with streets running in two dimensions and then the elevators in the buildings in the third dimension.

HAMILTON: Of course, the human brain has lots of folds and curves. So you have to imagine Manhattan bent into some odd shapes. But the underlying grid doesn't change. The streets intersect at 90-degree angles and the buildings rise vertically. Wedeen says once he saw the evidence of the brain's grid system, a lot of things began to make sense.

WEDEEN: I'd been looking at these pictures of these monkey brains for years, in a sense going nuts over how beautiful they look without being able to understand why the fibers were so often looking like sheets, why the curvatures were so well behaved and so organized.

HAMILTON: Wedeen says the grid model may help answer a question that has baffled geneticists and biologists: How can a relatively small number of genes contain the blueprint for something as complex as the human brain? Wedeen thinks he knows the answer, and here it is. In a highly organized system with consistent rules, a blueprint can use shorthand. It doesn't have to describe every detail.

WEDEEN: The grid structure exactly shows how simple recipes can produce a very complicated outcome.

HAMILTON: Wedeen says the grid may also help explain how the rudimentary brain of a flatworm evolved into the complex brain found in people. He says the grid system allows a species to gradually add new functions to its brain, much the way an architect adds floors to a building or a city planner adds new streets.

WEDEEN: And so you actually see the tools through which evolution builds a complicated human brain from more simply constructed ancestral brains.

HAMILTON: Not everyone thinks it's that simple, though. David Van Essen of Washington University in St. Louis says the results are surprising and intriguing, but not yet certain.

DR. DAVID VAN ESSEN: The evidence for their hypothesis is strong to some degree, though in a couple of important ways, I think they may have oversimplified the story.

HAMILTON: Take all those 90-degree intersections, for example. Van Essen says not everything is perpendicular. Other studies show that the brain's structure also includes some diagonal pathways. So Van Essen says it's possible the brain is neither spaghetti nor a perfect grid.

ESSEN: I expect it will turn out to be somewhere in between.

HAMILTON: The answer is coming soon. That's thanks to something called the Human Connectome Project. It's a five-year brain mapping effort supported by the National Institutes of Health. Van Essen says the project should help explain how brain wiring makes us who we are and what goes wrong in disorders like autism and Alzheimer's disease. The new research appears in the journal Science. Jon Hamilton, NPR News.

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