Not all brain regions are created equal ? instead, a "rich club" of 12 well-connected hubs orchestrates everything that goes on between your ears. This elite cabal could be what gives us consciousness, and might be involved in disorders such as schizophrenia and Alzheimer's disease.
As part of an ongoing effort to map
The researchers used a technique called diffusion tensor imaging to track the movements of water through 82 separate areas of the brain and their interconnecting neurons. They found 12 areas of the brain had significantly more connections than all the others, both to other regions and among themselves.
"These 12 regions have twice the connections of other brain regions, and they're more strongly connected to each other than to other regions," says Van den Heuvel. "If we wanted to look for consciousness in the brain, I would bet on it turning out to be this rich club," he adds.
Members of the elite
The elite group consists of six pairs of identical regions, with one of each pair in each hemisphere of the brain. Each member is known to accept only preprocessed, high-order information, rather than raw incoming sensory data.
Best connected of all is the precuneus, an area at the back of the brain. Van den Heuvel says its function is not well understood, but thinks that it acts as an "integrator region" collating high-level information from all over the brain.
Another prominent hub is the superior frontal cortex, which plans actions in response to events and governs where you should focus your attention. The superior parietal cortex ? the third hub ? is linked to the visual cortex and registers where different objects in your immediate vicinity are.
To bring memory into the equation, the hippocampus is another hub ? that's where memories are processed, stored and consolidated. The fifth member of the club is the thalamus, which, among other things, interlinks visual processes; the last member, the putamen, coordinates movement.
Together the hubs enable the brain to constantly assess, prioritise and filter incoming information, and then puts it all together to make decisions about what to do next.
This network makes the way the brain functions more robust overall, but it could also leave the entire system vulnerable to breakdown if key hubs are damaged or disabled, says Van den Heuvel.
Downfall of the rich
After mapping the connections, Van den Heuvel's team manipulated the data to see what might happen if parts of the rich club were damaged. The simulated brain lost three times as much function if the elite hubs were taken out than if random parts of the brain were lost.
"If [one of these] regions goes down, it can take the others down too, just like when banks failed in the global economic crisis," says Van den Heuvel.
Such vulnerability probably has great relevance to diseases such as schizophrenia, which is known to result from faulty connectivity within the brain, he says. It could also have role in Alzheimer's disease, Parkinson's disease and autism.
With further refinement, the connectome could be a useful model showing how connections become disrupted in different disease states, and how they might be restored.
"The human brain is extraordinarily complex, yet it works efficiently, and a major challenge has been to discover principles of brain wiring and organisation that explain this," says Randy Buckner, a neuroscientist at Harvard University.
"What Van den Heuvel and Sporns show is that some regions of the brain are embedded in densely connected networks ? so-called rich clubs ? that may act together as a functional unit," says Buckner. "Such an organisation might help explain how complex networks of brain regions can work together efficiently."
Other teams, such as that led by Jeffrey Lichtman of Harvard University, are mapping the brain in even finer detail, cell by cell.
Journal reference: Journal of Neuroscience, DOI: 10.1523/jneurosci.3539-11.2011
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lord monckton lord monckton andy kaufman october 21 2011 ohio ohio john beck
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