What’s a Connectome?


I’ll give you two hints:

1) You cannot buy one.

2) You cannot eat one.

Despite these two facts (and the fact that my word processor strongly suspects “connectome” is not a word at all), I will bravely attempt to blog about what a connectome is.

Because the concept of a connectome, I think, is about to radically change the way we talk about consciousness. And unconsciousness. And death. In fact, I’m going to go ahead and say that ten years from now, it’s going to be hard to remember how we talked about any of those things without the concept of a connectome.

A digitally rendered map of a connectome. Not as sexy as the real thing, but still...

If the word “connectome” was a person, though, it would have just barely graduated from kindergarten. The neuroscientist Olaf Sporns coined it in a jaw-dropping (for me, anyway) 2005 paper titled, “The Human Connectome: A Structural Description of the Human Brain.”

While “The Human Connectome” sounds like an awesome title for a horror movie, the title of the paper conveys a fairly clear idea of what Sporns meant by the term. Still, I like how he defines it in his own words:

The connectome is the complete description of the structural connectivity (the physical wiring) of an organism’s nervous system.

It’s as simple (and as face-smashingly complex) as that.

In fact, it’s so complex that Sporns himself said, “The full connectome, at cellular resolution, seems presently out of reach, at least for the human brain.”

But, this being science, it wasn’t long before other researchers started taking that statement as a challenge.

In 2008, the MIT neuroscientist (and cognitive scientist; and theoretical physicist; and mathematician; and undefeated master of 7 martial-arts styles named after poisonous animals) Sebastian Seung tackled the concept with his paper “Connectomics: Tracing the Wires of the Brain.” After a few introductory paragraphs, Seung got down to business:

The structure of the brain is extraordinarily complex. … But I and others are now optimistic that the connectome will eventually be transformed from dream into reality. A new field of neuroscience will be created: “connectomics.”

Now, even if you’re not a professional genius like Seung, you can tell that what he’s saying boils down to, “Yeah, that thing we’ve all been hearing is out of reach? I’m actually reaching for it right now; and, oh yeah, I’m gonna have to invent a new scientific field to deal with it.”

So, what have Seung and his team been up to since 2008? Oh, nothing much; just taking thousands of slices of mouse brains and reconstructing every single synapse in 3-D.

He admits it’s going to take a while: it’s roughly estimated that the human brain has anywhere from 100 billion to 1010 neurons, linked by anywhere from 100 trillion to 1014 synaptic connections. Yeah, that’s a 10 followed by 14 zeroes – far more than the number of genes in a human genome.

But Seung isn’t just going to wait around for his lab assistants to hand-dye every neuron in a mouse brain – he and his colleagues are also designing computer systems that will be powerful enough to map billions of neural connections simultaneously. This, he says, will allow them to explore complex synaptic chains in real time.

Also, it will pretty much be the neuroscientific equivalent of Real Steel.

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