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friday :: november 17, 2006
neural noise represents the uncertainty of the world

How can it be that our neurons, which are responsible for our crystal-clear thoughts, seem to fire in utterly random ways? A study by researchers at the University of Rochester shows that the brain's cortex uses seemingly chaotic, or "noisy," signals to represent the ambiguities of the real world--and that this noise dramatically enhances the brain's processing, enabling us to make decisions in an uncertain world.

Alex Pouget work for the first time connects two of the brain's biggest mysteries; why it's so noisy, and how it can perform such complex calculations. As counter-intuitive as it sounds, the noise seems integral to making those calculations possible.

In the last decade, Pouget and his colleagues have blazed a new path to understanding our gray matter. The traditional approach has assumed the brain uses the same method computation in general had used up until the mid-80s: You see an image and you relate that image to one stored in your head. But the reality of the cranial world seems to be a confusing array of possibilities and probabilities, all of which are somehow, mysteriously, properly calculated.

The science of drawing answers from such a variety of probabilities is called Bayesian computing, after minister Thomas Bayes who founded the unusual branch of math 150 years ago. Pouget says that when we seem to be struck by an idea from out of the blue, our brain has actually just resolved many probabilities its been fervently calculating.

"We've known for several years that at the behavioral level, we're 'Bayes optimal,' meaning we are excellent at taking various bits of probability information, weighing their relative worth, and coming to a good conclusion quickly," says Pouget. "But we've always been at a loss to explain how our brains are able to conduct such complex Bayesian computations so easily."

Bayesian computing can be done most efficiently when data is formatted in what's called "Poisson distribution." And the neural noise, Pouget noticed, looked suspiciously like this optimal distribution. This idea set Pouget and his team into investigating whether our neurons' noise really fits this Poisson distribution, and in his current paper he found that it fit extremely well.

"The cortex appears wired at its foundation to run Bayesian computations as efficiently as can be possible," says Pouget. His paper says the uncertainty of the real world is represented by this noise, and the noise itself is in a format that reduces the resources needed to compute it. Anyone familiar with log tables and slide rules knows that while multiplying large numbers is difficult, adding them with log tables is relatively undemanding. The brain is apparently designed in a similar manner--"coding" the possibilities it encounters into a format that makes it tremendously easier to compute an answer. >from *Mysterious 'neural noise' actually primes brain for peak performance*. November 10, 2006

related context
how the brain reflects onto itself the actions of others. october 6, 2006
> brain adaptive rewiring. august 18, 2006
> how brain cells work. april 28, 2006
> disorder-induced synchronization. april 14, 2006
> why the brain has gray and white matter. january 27, 2006
> how the brain makes a whole out of parts. january 17, 2006
> brain is a dynamic network. october 15, 2003
> mental operating system. january 4, 2002

make some neural noise boys

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