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A Neuroscientist's Quest to Reverse Engineer the Human Brain

M.I.T. scientist Sebastian Seung describes the audacious plan to find the connectome--a map of every single neuron in the brain. Here, he says, is the secret of human identity

By Gareth Cook  | March 20, 2012 | 8

SEBASTIAN SEUNG

What makes us who we are? Where is our personal history recorded, or our hopes? What explains autism or schiziphrenia or remarkable genius? Sebastian Seung argues that it’s all in the connections our neurons make. In his new book, Connectome , he argues that technology has now reached a point where it is conceivable to start mapping at least portions of the connectome. It’s a daunting task, he says, but without it, neuroscience will be stuck. He answered questions from Mind Matters editor Gareth Cook.  

Cook: Mapping the connectome seems like an almost impossibly difficult challenge. Critics say that you will may never succeed, or that if you do it will take decades, and we can't put neuroscience on hold for that long.

Seung: Indeed, mapping an entire human connectome is one of the greatest technological challenges of all time. Just imaging all of a human brain with electron microscopes would be difficult enough.  This would yield about one zettabyte of data, which roughly equals the world's current volume of digital content.  Then analyzing the images to extract the connectome would be even more demanding. Yet I believe that we will eventually prevail. Success will not come with a sudden bang but rather through sustained growth over time. I imagine that the speed of mapping connectomes will double every year or two. If so, then it will become possible to map an entire human connectome within a few decades.  There are similar success stories for other technologies.  Computers have improved at this rate for the past half century.  DNA sequencing has advanced similarly for the past forty years, and accelerated even further over the past decade.

That being said, such speculation about the far future is just for fun, and is actually beside the point. Even if we never succeed in mapping an entire human connectome, we will learn a tremendous amount by mapping connections in small chunks of human or animal brains.  This trend has already begun. Exciting developments in connectomics are happening right now; we don't have to sit around waiting for the future.

Cook:  Is there any way the research can be accelerated?  

Seung: We invite the public to visit a web site called EyeWire, where you can help map the connectome of the retina, the sheet of neural tissue at the back of the eye.  You don't need specialized training to participate, because EyeWire is like a virtual coloring book with pages that are images of the retina.  (The images were taken with an electron microscope in the laboratory of our German collaborator, Winfried Denk.) Your task is to color in neurons, and you already know how to do this: just stay inside the boundaries. In this way, you will trace the "wires" of the retina, the branches of its neurons.  This is the most laborious task required for mapping a connectome. (Another important task is identifying synapses, the tiny junctions at which neurons communicate with each other.)  

EyeWire's coloring book is so vast that no single person could live long enough to manually color the neurons.  We have sped up the process in two ways. First, artificial intelligence (AI) does most of the coloring automatically. You just have to guide the AI by a few mouse clicks here and there. Second, the coloring game is fun or even addictive to some people. Perhaps it's because the organic forms of neurons are mesmerizing.  Or maybe it's because the game is challenging; at some image locations it can be difficult to decide whether there is a boundary between two neurons, i.e., whether to continue coloring or to stop. EyeWire users tend to improve with practice at such decisions, because they gradually learn from experience how neurons are shaped.