'Is This Virtual Worm the First Sign of the Singularity' by Alexis Madrigal at the Atlantic May 17, 2013 (poor title, but good article) describes efforts to computationally model relatively simple life form, the C. elegans worm. The project raises interesting questions about a number of things, including what is life? and what constitutes understanding?
"If you're going to understand a nervous system or, more humbly, how a neural circuit works, you can look at it and stick electrodes in it and find out what kind of receptor or transmitter it has," said John White, who built the first map of C. elegans's neural anatomy, and recently started contributing to the project. "But until you can quantify and put the whole thing into a computer and simulate it and show your computer model can behave in the same way as the real one, I don't think you can say you understand it."This species of worm apparently has 959 cells, 302 of which are neurons. These neurons form approximately 10,000 connections. Part of what is unknown is just how much of the behavior of each cell needs to be fully modeled in order to simulate the worm's behavior. I think it's probably a pretty good place to start.
I asked several researchers whether simulating the worm was possible. "It's really a difficult thing to say whether it's possible," said Steven Cook, a graduate student at Yale who has worked on C. elegans connectomics. But, he admitted, "I'm optimistic that if we're starting with 302 neurons and 10,000 synapses we'll be able to understand its behavior from a modeling perspective." And, in any case, "If we can't model a worm, I don't know how we can model a human, monkey, or cat brain."