February 13th, 2012
Get your mind ready for a new term that seems to be gaining some currency – “connectome.” When I first encountered the word, I understood that it was about connections in the brain but for some reason I encoded the word as “connect to me.” But the final emphasis is on “tome” as in “home” not “to me,” so the word sounds like (and is meant to evoke the sense of) the genome. The term suggests that the power of the brain is not to be found in its component parts, but in the way that these component parts are connected.
The term was first coined by Olaf Sporns (U. of Indiana) in a 2005 paper entitled “The Human Connectome: A Structural Description of the Human Brain.” For Sporns, the connectome refers to a mapping of connections between regions of the brain. Sporns called for research that would provide a “comprehensive structural description of the network of elements and connections forming the human brain.” And, he proposed to call this dataset the “human connectome.”
Sporn argued that the mapping of regional connections would significantly “increase our understanding of how functional brain states emerge from their underlying structural substrate.” In 2010, the U.S. National Institutes of Health (NIH) launched the $30 million Human Connectome Project to map these regional connections.
Sebastian Seung, a young MIT professor and researcher feels that we need to go one step farther, mapping not only regions of the brain, but also mapping each and every neuronal connection. We have a hundred billion neurons in the brain, and a thousand times more connections, so Seung’s goal is daunting, but he thinks it is possible in the future. He discusses his ideas in his first book called “Connectome.”
I spoke with Seung at a book reading at Washington DC’s well-known independent book store, Politics and Prose. Seung is a Professor of Computational Neuroscience and Physics at MIT and an Investigator at the Howard Hughes Medical Institute. He is handsome, witty, prodigiously smart and in his a spiffy jacket, jeans and shiny gold sneakers, displays an unassuming charm. Candidly, this young thinker looks much too young to have achieved such status, but is his ideas have already reached TED audiences and his book will certainly continue to intrigue others.
Sueng and his MIT colleagues are currently developing techniques that he hopes will eventually map all of the neuronal connections in the brain. Seung showed slides of a labor intensive technique he developed that colorizes thin slices of brain tissue and then pieces them together, one slice at a time, to construct the locations of neurons and their connection points, the synapses. For additional background I suggest a few minutes viewing that TED video online called “Sebastian Seung: I am My Connectome.” And, also check out a “citizen science” project put together by Seung, called Eyewire, (http://eyewire.org/) where you can help map the neuronal structure of the human retina.
I asked Seung if we will ever be able to map neuronal connections in a living brain. He said the hope is to use ever more powerful neuroimaging machines to chart neuronal connections in living, active brains. The current technology, he explained, does not get anywhere near the resolution that is needed but improvements to the technology are in the works.
I had been curious whether glial cells might play a role in the connectome research. Glial cells make up an estimated 80% or so of the brain and they were once thought to be little more than structural helpers for the neurons. But recent research by Douglas Fields (see his book, The Other Brain) and others clearly demonstrates that glial cells communicate with each other and also communicate with neurons. They play a much more important role in brain processing than had previously been imagined. When I inquired about a the role of glial cells in the human connectome, Sueng said that while his current book focuses exclusively on neuronal connections, glial cells would clearly need to be factored into the understanding of the connectome.
Sueng likes to say that “you are your connectome,” meaning that our personal identity is encoded in the pattern of connections between neurons. These basic patterns are initially established by our inherited genes, but are constantly being modified by experience and interaction with the environment. Seung summarizes the types of change that are possible by offering “four R’s:”
Reweighting means changes in the strengths of synapses.
Reconnection is the creation and elimination of synapses.
Rewiring is the creation and elimination of neural branches.
Regeneration is the creation and elimination of neurons.
To understand how the brain produces feelings of love and compassion, for example, or why one brain is more creative than another, we will need to understand how the active connections in the brain animate the various functional areas. It will be fascinating to monitor the progress of The Human Connectome Project as well as the pioneering work of Sebastian Seung and his colleagues at MIT.
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