06 March 2008

Top Down Brain, Bottom Up Brain

Cognitive Science has embarked upon the epic quest to understand--and recreate--a functioning "human-equivalent" brain. With such a daunting task of unprecedented magnitude, different teams of scientists are approaching the problem from different directions. A UC Berkeley team used an fMRI (functional magnetic resonance imaging) scanner to learn how the visual cortex (occipital lobe) of the brain decodes visual images.
Writing in the journal Nature, the scientists, led by Dr Jack Gallant from the University of California at Berkeley, said: "Our results suggest that it may soon be possible to reconstruct a picture of a person's visual experience from measurements of brain activity alone. Imagine a general brain-reading device that could reconstruct a picture of a person's visual experience at any moment in time."

...The technique relies on functional magnetic resonance imaging (fMRI), a standard technique that creates images of brain activity based on changes in blood flow to different brain regions. The first step is to train the software decoder by scanning a subject's visual cortex while they view thousands of images over five hours. This teaches the decoder how that person's brain codes visual information. The next stage is to take a new set of images and use the decoder to predict the brain activity it would expect if the subject was viewing each of them. Finally, the subject views images from this second set while in the scanner. "We simply look through the list of predicted activities to see which one is most similar to the observed activity, and that's our guess," said Gallant.

...The team estimate that if they used 1bn images (roughly the number on Google) it would have a success rate of 20%. With that many images, Gallant said, the software is close to doing true image reconstruction - working out what you are seeing from scratch. "There is no reason we shouldn't be able to solve this problem ... That's what we are working on now."___Guardian

A better understanding of brain coding for various tasks done by different parts of the brain, should facilitate better neurochips to serve as temporary "neural-scaffolding" after stroke or brain injury. The neurochip would allow continued brain processing for the damaged parts of the brain, while ongoing stimulation encourages natural brain connections to re-form.The opposite, bottom-up approach to understanding the brain is being done by IBM researchers in Switzerland. The researchers are attempting to "recreate", or simulate a rat brain cortex with advanced silicon parallel processors.
In the basement of a university in Lausanne, Switzerland sit four black boxes, each about the size of a refrigerator, and filled with 2,000 IBM microchips stacked in repeating rows. Together they form the processing core of a machine that can handle 22.8 trillion operations per second. It contains no moving parts and is eerily silent.

...Each of its microchips has been programmed to act just like a real neuron in a real brain. The behavior of the computer replicates, with shocking precision, the cellular events unfolding inside a mind. "This is the first model of the brain that has been built from the bottom-up," says Henry Markram, a neuroscientist at Ecole Polytechnique Fédérale de Lausanne (EPFL) and the director of the Blue Brain project. "There are lots of models out there, but this is the only one that is totally biologically accurate. We began with the most basic facts about the brain and just worked from there."

Every brain is made of the same basic parts. A sensory cell in a sea slug works just like a cortical neuron in a human brain. It relies on the same neurotransmitters and ion channels and enzymes. Evolution only innovates when it needs to, and the neuron is a perfect piece of design...In theory, this meant that once the Blue Brain team created an accurate model of a single neuron, they could multiply it to get a three-dimensional slice of brain.

...After assembling a three-dimensional model of 10,000 virtual neurons, the scientists began feeding the simulation electrical impulses, which were designed to replicate the currents constantly rippling through a real rat brain. Because the model focused on one particular kind of neural circuit—a neocortical column in the somatosensory cortex of a two-week-old rat—the scientists could feed the supercomputer the same sort of electrical stimulation that a newborn rat would actually experience.

It didn't take long before the model reacted. After only a few electrical jolts, the artificial neural circuit began to act just like a real neural circuit. Clusters of connected neurons began to fire in close synchrony: the cells were wiring themselves together. Different cell types obeyed their genetic instructions. The scientists could see the cellular looms flash and then fade as the cells wove themselves into meaningful patterns. Dendrites reached out to each other, like branches looking for light. "This all happened on its own," Markram says. "It was entirely spontaneous." ___Seed__via__NextBigFuture
Read the full article at the link above.

Of course, that is just a bare beginning in the approach to simulating a real rat brain. A human brain will be much harder. Still, there is much to be said for the bottom-up approach.

The goal is for researchers taking opposite approaches in understanding the brain to meet somewhere in the middle--like the US intercontinental railroad builders. The reality will probably be more interesting. We will likely see the two approaches feeding off each other--each result from one suggesting new experiments for the other.

Both approaches rely largely upon the ability of processor chips to analyse information, and put it in a form that allows the human brains of the researchers to generate logical hypotheses for testing and falsifying. The final goal of understanding human cognition well enough to recreate it in a machine, is still some distance off. Expect significant spinoffs to occur from such research long before the final goal is reached.

Labels: , ,

Bookmark and Share

0 Comments:

Post a Comment

“During times of universal deceit, telling the truth becomes a revolutionary act” _George Orwell

Links to this post:

Create a Link

<< Home

Newer Posts Older Posts
``