A lot of publications have picked up this IBM press release, resulting in what must be some of the worst science reporting of the year. Modha and his colleagues at IBM have not simulated a mouse or rat brain. No one can do that at present; the wiring diagram isn't known at that level of detail.
What they did was simulate a huge, randomly-wired network of grossly simplified "neurons" on a supercomputer. The number of units was roughly comparable to the number of neurons in rat cortex, and the statistics of short vs. long-range connections (intra vs. inter-cluster connections) was vaguely suggestive of the organization of cortex, But they used single-compartment, integrate-and-fire neurons that are vastly simpler than real neurons, which do lots of nonlinear processing in their complex dendritic trees. So their network didn't actually compute anything at all. What it did, basically, was oscillate.
Calling this a simulation of a severely brain-damaged baby rat being run through a blender while having an epileptic seizure would still imply far too much realism to this cartoon.
The Modha group's work is a useful step toward the long-term goal of eventually building large-scale simulations of cortical circuitry on a supercomputer. But to report that they've presently produced a simulation of "a mouse brain", as some of the news articles are saying, is ludicrous.
The amount of neuroscience that needs to be done, the number of people required, and the time and costs it will take to produce an accurate simulation of even a mouse brain are orders of magnitude larger than this modest $4.9 million research contract. I'm amazed that technology reporters can be so gullible.