28 November 2007

Rat Cortical Column Simulation Update: From Here to an Artificial Brain?

One of the holy grails of neuroscience is the creation of an accurate simulation of mammalian brain cortex. Swiss researchers have been working on the "Blue Brain" project since 2005, and are collaborating with IBM researchers to simulate the neocortex.
By mimicking the behavior of the brain down to the individual neuron, the researchers aim to create a modeling tool that can be used by neuroscientists to run experiments, test hypotheses, and analyze the effects of drugs more efficiently than they could using real brain tissue.

The model of part of the brain was completed last year, says Markram. But now, after extensive testing comparing its behavior with results from biological experiments, he is satisfied that the simulation is accurate enough that the researchers can proceed with the rest of the brain.

"It's amazing work," says Thomas Serre, a computational-neuroscience researcher at MIT. "This is likely to have a tremendous impact on neuroscience."

The neocortical column is considered the functional building block of the mammalian cortex--a logical unit of brain organisation to begin a useful brain simulation project.
The project began with the initial goal of modeling the 10,000 neurons and 30 million synaptic connections that make up a rat's neocortical column, the main building block of a mammal's cortex. The neocortical column was chosen as a starting point because it is widely recognized as being particularly complex, with a heterogeneous structure consisting of many different types of synapse and ion channels. "There's no point in dreaming about modeling the brain if you can't model a small part of it," says Markram.

The model itself is based on 15 years' worth of experimental data on neuronal morphology, gene expression, ion channels, synaptic connectivity, and electrophysiological recordings of the neocortical columns of rats. Software tools were then developed to process this information and automatically reconstruct physiologically accurate 3-D models of neurons and their interconnections.

The researchers now think they have their neocortical column model well enough perfected to begin working on an entire mammalian "brain." They think they can model a mammalian brain realistically within 3 years, but respected neuro-researcher Christof Koch says "not so fast!"
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.

The simulation is at a cellular level, and the researchers want to go deeper to the molecular level. This will put a tremendous strain on the computational infrastructure of the system. And it is not clear what is to be gained at this early stage by going to molecular resolution. Particularly when the cortical function appears to be at least partially based upon oscillatory phase-locking of assembles of neurons, such as columns and columnar groups.

Perhaps the Swiss researchers' "bottom-up" approach, combined with "top-down" approaches by people such as Jeff Hawkins, will begin to simulate some of the function of the human neocortex within the next 15 years. Perhaps.

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