Fewer are familiar with the similar-sounding word "connectome" (pronounced con-NEC-tohm). I didn't hear it until fall 2007, when, as a science journalism fellow at the Massachusetts Institute of Technology, I watched a jaw-dropping video in an introductory neuroscience course. The instructor was an intense, soft-spoken young brain scientist named Sebastian Seung, who favored artsy T-shirts and immaculate Technicolor sneakers.
But it was the video that caught everyone's eye that day.
The connectome, Seung explained, is the totality of the connections among the human brain's 100 billion neurons. It's the brain's wiring blueprint, a spidery, intricate latticework of nerve fibers and synapses over which -- in theory, at least -- our thoughts race, our emotions flicker and our memories circulate like drivers on some endless, and endlessly complex, highway system.
Mapping the human connectome -- which science is only beginning to figure out how to do -- would outshine even the genome-cracking effort. It could illuminate how each of our uniquely individualized wiring patterns shapes the way we think and who we are. Seung's video was an early attempt at tracing the wiring of just a smidgen of a rabbit's brain. By stitching together 2-D cross sections of the tiny brain segment taken with a powerful electron microscope, a 3-D model of this bit of the rabbit connectome emerged. It looked like a tangle of multihued chewing gum strands.
At the time, we students barely grasped what we were seeing. Five years later, Seung elaborates in "Connectome," his bracing, mind-expanding report from neuroscience's razor edge. Accessible, witty, imminently logical and at times poetic, "Connectome" establishes Seung as an important new researcher, philosopher and popularizer of brain science. It puts him on par with cosmology's Brian Greene and the late Carl Sagan.
"Connectome" begins with a history lesson, recapping the 19th-century obsession among phrenologists to link the brain's size to intelligence, and moving into the 20th-century advances in deciphering neuron-to-neuron cross talk.
Seung then gently walks readers through the basics of connectomics, explaining how genes carry the blueprint for the brain's initial state, but the connections that neurons forge and prune, strengthen and weaken, shape and reshape, throughout our lives are what encodes the essence of us. Minds differ, he argues, because connectomes differ.
"Since the connectome defines the pathways along which neural activity can flow, we might regard it as the streambed of consciousness," Seung writes. "The metaphor is a powerful one. Over a long period of time, in the same way that the water of the stream slowly shapes the bed, neural activity changes the connectome. The two notions of the self -- as both the fast-moving, ever-changing stream and the more stable but slowly transforming streambed -- are thus inextricably linked."
Better understanding this could help us figure out how we store and recall memories, Seung contends. Comparing brain wiring could clarify the origin -- and perhaps suggest improved treatments for -- conditions like schizophrenia and autism, which are thought to involve connection problems.
"To understand why minds differ, we have to see better how brains differ," he writes. "That's why comparing connectomes is so crucial."
Seung's logic is persuasive, but as he candidly admits, it's largely theoretical. Scientists so far have managed to map the connectome of only one organism: the humble, raindrop-small roundworm C. elegans. Though the worm has just 300 neurons, finding and analyzing all the connections took South African researchers more than a dozen years.
By contrast, the human brain may possess 100 trillion neural junctures, or synapses. Seung's MIT lab and other neuroscientists are working on ways of harnessing advanced computers to help with the connectome tracing. Once done, researchers will still need to decipher the electro-chemical messages zipping along the brain's myriad pathways.
Finding and analyzing the human connectome is a daunting, moonshot project that Seung acknowledges will require technological leaps. It could take the rest of the century.
He is frank about the challenges ahead, but his excitement shines through.
John Mangels is The Plain Dealer's science writer.