Study: Brain Connections Like Woven Fabric, Not Tangled Spaghetti

Updated at 2:56 PM, March 29th, 2012

Calling Neo. It doesn't matter if you choose the blue pill or the red pill, your brain is the matrix.

Forgive my funning with some very serious findings just out in the journal Science: Your brain's connections are not a tangled mass of spaghetti. Rather, they criss-cross each other in an orderly grid, "like the warp and weft of fabric," says Dr. Van Wedeen of Massachusetts General Hospital, the Martinos Center for Biomedical Imaging and Harvard Medical School.

But really, how could I help but think of a matrix — or the cinematic greatness of The Matrix? Another helpful image, from the National Institute of Mental Health's press release: The street map of Manhattan.

The brain appears to be wired more like the checkerboard streets of New York City than the curvy lanes of Columbia, Md., suggests a new brain imaging study. The most detailed images, to date, reveal a pervasive 3D grid structure with no diagonals, say scientists funded by the National Institutes of Health.

“Far from being just a tangle of wires, the brain’s connections turn out to be more like ribbon cables — folding 2D sheets of parallel neuronal fibers that cross paths at right angles, like the warp and weft of a fabric,” explained Van Wedeen... “This grid structure is continuous and consistent at all scales and across humans and other primate species.”

The discovery of this "astonishingly simple" structure of brain connections brought a ringing assessment from the chief of the National Institute of Mental Health, which helped fund the work: “Getting a high resolution wiring diagram of our brains is a landmark in human neuroanatomy,” said NIMH Director Thomas R. Insel in a press release. “This new technology may reveal individual differences in brain connections that could aid diagnosis and treatment of brain disorders.”

Dr. Wedeen describes his team's work and its potential implications in the video above. It helps to watch his hand gestures as he says:

"What we discovered is that the fiber architecture of the brain is more or less a simple as you can possibly imagine. Each pathway, rather than being an isolated pathway, is a component in a three-dimensional grid. The pathways in the top of the brain are all organized like woven sheets so that the fibers only run in two directions in the sheet and in a third direction perpendicular to the brain, and these sheets all stack together. So the entire connectivity of the brain follows three precisely defined directions.

Now, these directions are a little bit hard to spot, because in embryological life they're simple directions but then in the adult brain they get very folded and curled up, and so that surface of the brain that you see, with all its folds, has pulled the wires around with it, and so these three directions have now become greatly curved....

But fundamentally, the geometry of the brain is described by a three-dimensional grid...So as a result of this, we now have a way of seeing the structure of the brain as a single unified whole. It no longer seems like a bunch of uncorrelated or isolated connections. The entire connectome fits together into a single framework which expresses developmental rules, and, we speculate or hypothesize, functional rules as well."

I asked Dr. Wedeen to explain a bit more about his work. Please stay tuned for excerpts of our conversation. For now, more of the crystalline press release:

Knowledge gained from the study helped shape design specifications for the most powerful brain scanner of its kind, which was installed at MGH’s Martinos Center last fall. The new Connectom diffusion magnetic resonance imaging (MRI) scanner can visualize the networks of crisscrossing fibers – by which different parts of the brain communicate with each other – in 10-fold higher detail than conventional scanners, said Wedeen.

“This one-of-a-kind instrument is bringing into sharper focus an astonishingly simple architecture that makes sense in light of how the brain grows,” [Wedeen] explained. “The wiring of the mature brain appears to mirror three primal pathways established in embryonic development.”

As the brain gets wired up in early development, its connections form along perpendicular pathways, running horizontally, vertically and transversely. This grid structure appears to guide connectivity like lane markers on a highway, which would limit options for growing nerve fibers to change direction during development. If they can turn in just four directions: left, right, up or down, this may enforce a more efficient, orderly way for the fibers to find their proper connections – and for the structure to adapt through evolution, suggest the researchers.

Obtaining detailed images of these pathways in human brain has long eluded researchers, in part, because the human cortex, or outer mantle, develops many folds, nooks and crannies that obscure the structure of its connections. Although studies using chemical tracers in neural tracts of animal brains yielded hints of a grid structure, such invasive techniques could not be used in humans.

Wedeen’s team is part of a Human Connectome Project Harvard/MGH-UCLA consortium that is optimizing MRI technology to more accurately to image the pathways. In diffusion imaging, the scanner detects movement of water inside the fibers to reveal their locations. A high resolution technique called diffusion spectrum imaging (DSI) makes it possible to see the different orientations of multiple fibers that cross at a single location – the key to seeing the grid structure.

In the current study, researchers performed DSI scans on postmortem brains of four types of monkeys – rhesus, owl, marmoset and galago – and in living humans. They saw the same 2D sheet structure containing parallel fibers crossing paths everywhere in all of the brains – even in local path neighborhoods. The grid structure of cortex pathways was continuous with those of lower brain structures, including memory and emotion centers. The more complex human and rhesus brains showed more differentiation between pathways than simpler species.

Among immediate implications, the findings suggest a simplifying framework for understanding the brain’s structure, pathways and connectivity.
...
“Before, we had just driving directions. Now, we have a map showing how all the highways and byways are interconnected,” said Wedeen. “Brain wiring is not like the wiring in your basement, where it just needs to connect the right endpoints. Rather, the grid is the language of the brain and wiring and re-wiring work by modifying it.”

Carolyn Johnson describes the study in The Boston Globe. She writes:

Partha Mitra, a neuroscientist at Cold Spring Harbor Laboratory who was not involved in the research, said the effort to find the wiring diagram of the brain is important, but that the general findings of the paper are not surprising. He said he is interested in seeing a more quantitative description of the grid-like structures and validation of the findings using other techniques besides the imaging technology.

And Ed Yong writes on Discover Magazine's "Not Exactly Rocket Science" blog:

Opinion is divided on the new study. “It’s really ingenious what they’ve done,” says Tim Behrens from the University of Oxford, who is particularly impressed with the idea that the white matter forms interwoven sheets. “It’s really quite convincing,” he says. “There’s no way that the sheets are there by chance.”

David van Essen from Washington University in St Louis agrees, but he and Behrens both say that Wedeen’s technique is more sensitive at measuring right angles than other angles. They feel that the right-angled connections of the white matter remain to be proven.