The neuronal circuits were tested by simulating specific input stimuli and seeing how the circuits behaved, compared with those in biological experiments. Where gaps in knowledge appeared about how certain parts of the model were supposed to behave, the scientists went back to the lab and performed experiments to identify the kinds of behavior that needed to be reproduced. In fact, about a third of the team of 35 researchers was devoted to carrying out such experiments, says Markram.
Through an iterative process of testing, the simulation has gradually been refined to the point where Markram is confident that it behaves like a real neocortical column.
However, none of these results have so far been published in the peer-reviewed literature, says Christof Koch, a professor of biology and engineering at Caltech. And this is by no means the first computer model of the brain, he points out. “This is an evolutionary process rather than a revolutionary one,” he says. As long ago as 1989, Koch created a 10,000-neuron simulation, albeit in a far simpler model.
Furthermore, Koch is skeptical about how quickly the brain model can progress. Any claims that the human brain can be modeled within 10 years are so “ridiculous” that they are not worth discussing, he says.
Rat brains have about 200 million neurons, while human brains have in the region of 50 to 100 billion neurons. “That is a big scale-up,” admits Markram.
But he is confident that his model is robust enough to be expanded indefinitely. What’s more, he believes that the level of detail of the model can also be taken further. “It’s at quite a high resolution,” he says. “It’s still at a cellular level, but we want to look at the molecular level.” Doing so would enable simulation-based drug testing to be carried out by showing how specific molecules affect proteins, receptors, and enzymes.
“I wouldn’t be surprised if they could do it,” says Serre. “However, it’s not clear what they could get out of it,” he says. If you want this model to be useful, you have to be able to understand how the behavior relates to specific brain functions. So far, it is not clear that the Blue Brain project has done this, he says.