March 06 2008 / by AlFin
Category: Other Year: 2008 Month: Mar Rating: 11
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.” Top
Down“
Achieving this level of understanding of brain coding for
various tasks done by different parts of the brain, should
facilitate better neurochips which could 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.
Understanding the brain from the bottom-up is the goal of
IBM researchers in Switzerland:
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.”
Story Source>
_This piece has been cross-posted from Al Fin’s blog
Comment Thread ()
