You are your connectome


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First aired on Quirks & Quarks (14/4/12)


MIT computational neuroscientist Dr. Sebastian Seung likes to say, "I am my connectome." What he means by that is that human minds -- our memories, personalities and proclivities -- are all encoded in the billions of neurons and thousands of connections between each neuron. These neurons and connections make up the wiring of the human brain, that is, our "connectome." And it is here that we can find the information that makes us who we are. In his new book, Connectome: How the Brain's Wiring Makes Us Who We Are, Seung shows how the connectome is built and explores how neuroscientists are trying understand how the mind works, how mental disorders might result from mis-wiring of the connectome, and ultimately, how we might map the connectome if we were ever to understand it well enough.

What, exactly, is the connectome? In a recent interview with Quirks & Quarks, Seung likened it to a travel map, such as the ones you find at the back of in-flight magazines -- the maps that show all the connecting flights between cities that the airline offers. In the connectome, "imagine that every one of those cities is replaced by a neuron" and "every flight was replaced by a connection between those two neurons." Then multiply the number of cities and connections. By a lot. One cubic millimetre of our brain "has about a billion connections total between neurons." That, in essence, is your connectome.

How does the connectome explain our personality traits? Seung compares the neurons to an enchanted forest "where all your ideas and thoughts live." The neurons transmit signals, which encode "what you are thinking, feeling, perceiving right now." What is happening to you in the present moment is an active part of your brain activity. The past, such as learned information and memories, is static in the brain. They are "stored in the pattern of the connections between your neurons," Seung explained. When you recall that information, it "has to be transferred from the static connections" and is converted into brain activity. Storing memories "modifies connections", which is, in part, why each connectome is unique. Your connectome is made up of these static past experiences and the stimulated activity of the present and how the two interact to generate your individual thoughts, memories and experiences.

Not only do connectomes change from person to person, they change with time. Your connectome of today is different from your connectome from five years ago and will be different from your connectome from a year from now. "The difference between your connectome and my connectome would presumably have to do with the fact that we have different memories, different personalities and so on," Seung says. "The differences in your connectome from now to next year would be all the things you've learned in that year's time."

Why does all this matter? Understanding the connectome will allow scientists to better understand how learning and memory work -- which could lead to developments in education, trauma rehabilitation, mental health and more. But mapping the connectome is a daunting task. "Your connectome has a million times more connections than your genome has letters. There's so much more information," Seung says. "To find an entire human connectome is beyond the reach of our current technology." But Seung is undeterred. He believes mapping the connectome, even by focusing on "small chunks of brain" at a time, is essential for neuroscience to move forward.

"If we can see what's wrong, in a definitive way, that should give us a leg up on developing therapies for it."

The images below are used with the permission of Sebastian Seung. For the complete Brain Forest collection, visit the Connectome the Book website.