And you thought sequencing the human genome was a big job. MIT neuroscientist Sebastian Seung is proposing something even more Herculean: tracing the trillions of neuronal connections in the human brain, collectively known as the "connectome." He believes the connectome may hold the key to understanding the brain and the self. That follows from connectionism—the notion that learning, memory and personality are embedded in the brain's wiring. Like so much else in neuroscience, that's still hypothetical, and Sebastian is refreshingly candid about the limits of current understanding. We discussed what is and isn't known about the workings of neurons, how the brain's circuitry might encode information, the relevance of computer models, and artificial intelligence techniques that may help map the connectome. Also: the "Jennifer Aniston neuron," whether or not to freeze your posthumous head, and the cautionary tale of the South Park underpants gnomes.