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A semiconductor microchip has been used successfully to replace a neural circuit in slices of rat live brain tissue. It is designed to model hippocampus, a part of the brain.
This technique could ultimately be used to replace damaged brain tissue which may have been destroyed in an accident, during a stroke, or by neurodegenerative conditions such as Alzheimer’s disease. It is the first attempt to replace central brain regions dealing with cognitive functions such as learning or speech.
To achieve their result, Theodore Berger and his colleagues at the University of Southern California in Los Angeles, US, had to develop a system that would “read” real neural signals from healthy tissue, process them just as the lost brain tissue should, and pass on the resulting signals to the next brain area. They cut out the central part of the circuit in real rat brain slices and used a grid of miniature electrodes to feed signals in and out of their microchip. The signals produced by the intact brain slice and the prosthetic hippocampus matched in shape, timing and statistics, the team revealed at the Society for Neuroscience meeting in San Diego on Sunday.
“It proves you can take out a piece of a central brain region - a piece with real clinical interest - replace it with a chip, and get it to operate as it did before,” said Berger.
The team is now working towards testing their prosthetic device on a live rat, which they expect to do within three years. They are also developing a mathematical model of primate hippocampal activity, so that they can eventually move on to testing the device in monkeys.
Guenter Gross, at the University of North Texas in Denton, is impressed with the approach, but adds “the problem will be how to make the long-range connections". Even if the device can replace the local connections, he suggests, the hippocampus makes connections to many different brain regions. “There are intricate, complicated connections formed during development that cannot be replaced,” he says.
Another problem is that when a region of the brain is damaged, immune cells and brain cells called glia migrate into the damaged site. They will affect any attempt to bypass or replace the damaged tissue, says Gross.
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