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>Brain Cells, Silicon Chips Are Linked Electronically
>Part-Mechanical, Part-Living Circuit Created
>By Shankar Vedantam
>Washington Post Staff Writer
>Tuesday, August 28, 2001; Page A03
>Scientists for the first time have linked multiple brain cells with
>silicon chips to create a part-mechanical, part-living electronic circuit.
>To construct the partially living electronic circuit, scientists at the
>Max Planck Institute for Biochemistry in Germany managed to affix multiple
>snail neurons onto tiny transistor chips and demonstrated that the cells
>communicated with each other and with the chips.
>The advance is an important step toward a goal that is still more science
>fiction than science: to develop artificial retinas or prosthetic limbs
>that are extensions of the human nervous system. The idea is to combine
>the mechanical abilities of electronic circuits with the extraordinary
>complexity and intelligence of the human brain.
>Such combinations of biology and technology may not only one day help the
>blind to see and the paralyzed to move objects with their thoughts, but
>also help to build computers that are as inventive and adaptable as our
>own nervous systems and a generation of robots that might truly deserve to
>be called intelligent.
>Meshing nerve cells with electronics has become a hot new field in science
>-- and has long been a staple of science fiction. But what "Star Trek"
>accomplished in a stroke of the pen has proved harder to achieve in real life.
>"The nervous system is quite different than a computer," said Eve Marder,
>a professor of neuroscience at Brandeis University who studies how the
>brain adapts to change. "Many functions that are physically separate in a
>computer are carried out by the same piece of tissue" in the brain and
>The greatest challenge has been in building the interface between biology
>and technology. Nerve cells in the brain find each other, strengthen
>connections and build patterns through complex chemical signaling that is
>driven in part by the environment. Slice away some neurons, for example,
>and others will leap in to replace their function. No one understands how
>the brain learns to adapt to change, but it is a process that is as
>sophisticated as it is messy.
>Silicon chips, on the other hand, can perform specific functions with
>great reliability and speed, but have limited responsiveness to the
>environment and almost no ability to alter themselves according to need.
>"Things are constantly changing . . . processes are growing, there are
>substances called neuromodulators that change the properties of nerve
>cells and the strength of connections," said Marder. "That's the challenge
>of making a silicon-brain interface -- the rules of computation are not
>The German researchers used micropipettes to lift individual cells from
>the snail brain and then puff them out onto silicon chips that were
>layered with a kind of glue. The snail neurons, according to biophysicist
>Peter Fromherz, are a little larger than human or rat neurons and were
>therefore easier to work with.
>"They suck them out and then blow them onto the structure," said Astrid
>Prinz, a post-doctoral researcher at Brandeis University, who used to work
>with the German group. "It's a matter of practice to learn to handle
>individual cells. You have them in a little pipette with fluid. You blow
>them out and you can maneuver them. One guy in the lab made a little movie
>on how to blow cells."
>Each cell was positioned over a Field Effect Transistor, a device that is
>capable of amplifying tiny voltages, and a stimulator to prod the cell
>The process was repeated with some 20 cells over multiple transistors and
>stimulators. By using polymers, the German scientists built tiny picket
>fences around the neurons to keep them in place over the transistors --
>one of the great difficulties in building such circuits is that nerve
>cells tend to wander around, as they do in the brain.
>Neurons on this silicon base developed a connection between each other
>known as a synapse. When researchers stimulated one neuron, it released an
>electrical signal. That signal was detected by the transistor that the
>neuron sat on as well as the transistor beneath a second neuron -- showing
>that the electrical signal had passed from the chip to the first neuron,
>through a synapse to the second neuron and then converted back into
>electricity and the second transistor.
>"It's very primitive, but it's the first time that a neural network was
>directly interfaced with a silicon chip," said Fromherz, who published the
>results in today's issue of the Proceedings of the National Academy of
>Science. "It's a proof of principle experiment."
>The group, he said, was already working on linking greater numbers of
>neurons with more transistors. The real challenge, he said, lay in
>figuring out where exactly the neuron's synapse was relative to the
>transistor, and in developing techniques that could reliably construct
>larger circuits. Fromherz said plans were underway to build a system with
>15,000 neuron-transistor sites.
>When the number gets large enough, researchers hope they will begin to see
>the early glimmers of what actually happens in the brain: neurons forming
>complex connections that transmute electrical activity into computation,
>thoughts and maybe consciousness itself.
>© 2001 The Washington Post Company
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