In the EU and the USA, high-profile, high-budget programs are underway to simulate a human brain. While these produce some pretty pictures of simulations, they don't display much rigor or advancement of our understanding of how brains work.
In a profane, lengthy rant, an anonymous neuroscientist on Mathbabe shreds the idea and approach to human brain simulation, shedding light on how little we know about the subject.
(1) We have no fucking clue how to simulate a brain.
We can't simulate the brain of C. Elegans, a very well studied roundworm (first animal to have its genome sequenced) in which every animal has exactly the same 302-neuron brain (out of 959 total cells) and we know the wiring diagram and we have tons of data on how the animal behaves, including how it behaves if you kill this neuron or that neuron. Pretty much whatever data you want, we can generate it. And yet we don't know how this brain works. Simply put, data does not equal understanding. You might see a talk in which someone argues for some theory for a subnetwork of 6 or 8 neurons in this animal. Our state of understanding is that bad.
(2) We have no fucking clue how to wire up a brain.
Ok, we do have a macroscopic clue, this region connects to that region and so on. You can get beautiful pictures with methods like DTI, with a resolution of one cubic millimeter per voxel. Very detailed, right? Well, apart from DTI being a noisy and controversial method to begin with, remember that one cubic millimeter of brain required a supercomputer to simulate it (not worrying here about how worthless that "simulation" was), so any map with cubic-millimeter voxels is a very coarse map indeed. And microscopically, we have no clue. It looks pretty random. We collect statistics (with great difficulty), and do tons of measurements (also with great difficulty), but not on humans. Even for well studied animals such as cats, rats, and mice, it's anyone's guess what the fine structure of the connectivity matrix is. As an overly simplistic comparison, imagine taking statistics on the connectivity of transistors in a Pentium chip and then trying to make your own chip based on those statistics. There's just no way it's gonna work.
Guest post: Dirty Rant About The Human Brain Project