Circuit Diagrams of the Brain
It’s important to know which neurons are connected to each other to understand how the brain thinks.
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| R. Clay Reid, Professor of Neurobiology, Harvard Medical School |
The human brain would seem impossibly complex if we could see its billions of neurons, connected by trillions of branching nerve fibers. But thanks to new technologies in brain science, imaging, and computing, scientists can now create huge images of the brain in nanometer resolution. These will help us chart the brain’s circuits with the goal of one day mapping an entire mammalian brain.
The Harvard Center for Brain Science has launched an ambitious effort to build “circuit diagrams” that will show the connections between individual brain cells. Called “connectomes,” these 3-D images of the brain’s wiring could prove as fundamental to the understanding of the brain as genomes have been to the understanding of modern biology.
The Connectome Project, part of Harvard’s Initiative for Innovative Computing, was launched by my colleague Professor Jeff Lichtman and now includes an interdisciplinary team of neurobiologists, engineers and computer scientists. One goal is to map a one-cubic-millimeter portion of a mouse’s brain. That’s just one thousandth of the brain, but the 3-D image database of it will contain 200,000 individual neurons and perhaps a billion connections, and require 1000 terabytes of computer storage.
To speed up the task, we’ve built an electron microscope camera that photographs images of brain tissue 10 times faster than commercial systems. Lichtman’s group has built a new machine that cuts much larger and thinner slices of brain tissue, making it possible to create higher-resolution, panoramic images that can span most of a mouse’s brain. Microsoft Research, which has done extensive research on image processing, is providing resources to help stitch together and navigate these complex images.
These circuit diagrams of the brain could help answer important questions. We know, for example, that there are dozens of types of brain cells. And we know, roughly, the way information flows between these types. But just as diagrams are critical to understanding how an electronic device works, we need to know how individual neurons are connected to each other to understand how the brain thinks.
Circuit diagrams could also help us understand how connections in the brain change over time. A wasp’s brain is pre-wired to fly, for example, but it takes a child a whole year to learn to walk. What changes in brain connections make that learning possible?
It may be decades before we can map the trillions of connections in the mammalian brain, but it is already possible to imagine a time when we might identify defects in brain wiring that could help us understand conditions such as autism or the diseases of brain aging.
