Saturday, January 30, 2010

human connectome project

MIT | C. elegans, a tiny worm about a millimeter long, doesn’t have much of a brain, but it has a nervous system — one that comprises 302 nerve cells, or neurons, to be exact. In the 1970s, a team of researchers at Cambridge University decided to create a complete “wiring diagram” of how each of those neurons are connected to one another. Such wiring diagrams have recently been christened “connectomes,” drawing on their similarity to the genome, the total DNA sequence of an organism. The C. elegans connectome, reported in 1986, took more than a dozen years of tedious labor to find.

Now a handful of researchers scattered across the globe are tackling a much more ambitious project: to find connectomes of brains more like our own. The scientists, including several at MIT, are working on technologies needed to accelerate the slow and laborious process that the C. elegans researchers originally applied to worms. With these technologies, they intend to map the connectomes of our animal cousins, and eventually perhaps even those of humans. Their results could fundamentally alter our understanding of the brain.

Mapping the millions of miles of neuronal “wires” in the brain could help researchers understand how those neurons give rise to intelligence, personality and memory, says Sebastian Seung, professor of computational neuroscience at MIT. For the past three years, Seung and his students have been building tools that they hope will allow researchers to unravel some of those connections. To find connectomes, researchers will need to employ vast computing power to process images of the brain. But first, they need to teach the computers what to look for.

A tangled web
Piecing together connectomes requires analyzing vast numbers of electron microscopic images of brain slices and tracing the tangled connections between neurons, each of which can send projections to other cells several inches away.

At the Max Planck Institute for Medical Research in Heidelberg, Germany, neuroscientists in the laboratory of Winfried Denk have assembled a team of several dozen people to manually trace connections between neurons in the retina. It’s a painstaking process — each neuron takes hours to trace, and each must be traced by as many as 10 people, in order to catch careless errors. Using this manual approach, finding the connectome of just one cubic millimeter of brain would take tens of thousands of work-years, says Viren Jain, who recently completed his PhD in Seung’s lab. Fist tap Big Don.