HCP Principal Investigator David Van Essen appeared today on National Public Radio’s afternoon news program All Things Considered in an interview with Science reporter Jon Hamilton.
Dr. Van Essen commented on a new study appearing in the March 30 edition of Science by Van Wedeen at Harvard University/Massachusetts General Hospital and colleagues entitled “The Geometric Structure of the Brain Fiber Pathways”. The authors studied the brains of four non-human primate species and humans using diffusion MRI (a major imaging modality being employed in the HCP) to determine the architecture of white matter fiber tracts that connect brain regions to each other.
The authors propose that cerebral fiber pathways in the brain intersect perpendicular to each other, creating a three-dimensional grid layout. This architecture, Dr. Wedeen says, can explain how the brain evolved complexity over time:
The grid model could help answer a question that has baffled geneticists and biologists for years, Wedeen says: How can a relatively small number of genes contain the blueprint for something as complex as the human brain?
The answer may be that in a highly organized grid system with consistent rules, a genetic blueprint doesn’t have to describe every detail of the final product, he says.
“The grid structure shows how simple recipes can produce a very complicated outcome,” Wedeen says.
The grid also may help explain how the rudimentary brain of a flat worm evolved into the complex brain found in people, Wedeen says.
The grid system, he says, would allow a species to gradually add new functions to its brain much the way an architect adds extra floors to a building or a city planner adds new streets.
“So you actually see the tools through which evolution builds a complicated human brain from more simply constructed ancestral brains,” he says.
Dr. Van Essen responded to the study with some skepticism and optimism that clearer, more definitive answers for human brain architecture are coming soon with the efforts of the Human Connectome Project:
The results of the new study are surprising and intriguing, but not yet certain, says David Van Essen, a neuroscientist at Washington University School of Medicine in St. Louis.
“The evidence for their hypothesis is strong to some degree,” Van Essen says. But he adds that “in a couple of important ways I think they may have oversimplified the story.”
Take all those 90 degree intersections, for example.
Other studies show that the brain’s structure also includes some diagonal pathways as well, Van Essen says. So he says it’s possible the brain is neither pure spaghetti nor a perfect grid.
“I expect it will turn out to be somewhere in between,” he says.
A definitive answer about the structure of the brain’s wiring probably isn’t far off, Van Essen says, thanks to something called the Human Connectome Project. It’s a five-year brain-mapping effort supported by the National Institutes of Health.
Those findings should help explain how our brain wiring makes us who we are, Van Essen says, and what goes wrong in disorders like autism and Alzheimer’s disease.
Read and listen to the NPR story in its entirety here.
Read the full text of the article “The Geometric Structure of the Brain Fiber Pathways” in Science here.