How Your Brain is Like a City

Image credit: Van Wedeen, M.D., Martinos Center and Dept. of Radiology, Massachusetts General Hospital and Harvard University Medical School

The link between the two isn’t metaphorical in this case- according to a new study, the connective foundations of our brain look as though they were designed by a grid-focused city planner.

Researchers used cutting-edge imaging technology to look at places where the fibers that carry messages from one part of the brain to another intersect. And they found a remarkably organized three-dimensional grid, according to Van Wedeen of Harvard Medical School, the study’s lead author.

The grid is a bit like Manhattan, Wedeen says, “with streets running in two dimensions and then the elevators in the buildings in the third dimension.”

Obviously this brain-city would not fit on a single plane- the human brain has many folds and curves. So, Wedeen says, “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.”

It sounds to me like that brain is less like Manhattan, and more like the city pictured during this famous scene from Inception:

 

This city-like grid represents a significant shift from the traditional model of the brain’s wiring. Wedeen explains that in the old view, “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.”

This new model for understanding the internal structure of the brain may help to explain how a relatively small number of genes contain the blueprint for something as complex as the human brain- a question that has stumped geneticists for years.

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, Wedeen says. “The grid system 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.”

There remains some uncertainty regarding whether the entire brain is actually laid out in this way. Weeden was only able to resolve the grid for about a quarter of the human brain, mostly in the deepest parts. Some researchers have expressed the opinion that their model is oversimplified, or that while the grid may exist, it is combined with other, crisscrossing connections as well.

The debate may be resolved within 5 years- that is the timetable for the US National Institute of Health’s Human Connectome Project, which aims to map all the brain’s wiring and demonstrate its connection to mental health over the next half-decade.

Sources:  Research abstract: “The Geometric Structure of the Brain Fiber Pathways” - Science Magazine

Press release: “Brain Wiring a No-Brainer?” 

The Human Connectome Project