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First artificial hippocampus unveiled

18 March, 2003

Researchers in California have unveiled an artificial hippocampus - a silicon chip implant that will perform the same processes as the damaged part of the brain it is replacing.

The chip will first be tested on tissue from rats' brains, and then on live animals and if successful, it will then be tested as a way to help people who have suffered brain damage due to stroke, epilepsy or Alzheimer's Disease.

Team leader Theodore Berger of the University of Southern California said that the job of the hippocampus appears to be to 'encode' experiences so they can be stored as long-term memories elsewhere in the brain. He added:

"If you lose your hippocampus you only lose the ability to store new memories. That offers a relatively simple and safe way to test the device: if someone with the prosthesis regains the ability to store new memories, then it's safe to assume it works."

However, the study team acknowledges that any device that mimics the brain raises ethical issues. The brain not only affects memory, but your mood, awareness and consciousness - parts of your fundamental identity, says ethicist Joel Anderson at Washington University in St Louis.

The mechanics of how the hippocampus encodes information has yet to be discovered, so the team simply copied its behaviour. Slices of rat hippocampus were stimulated with electrical signals, millions of times over, until they could be sure which electrical input produces a corresponding output. Putting the information from various slices together gave the team a mathematical model of the entire hippocampus.

They then programmed the model onto a chip, which in a human patient would sit on the skull rather than inside the brain. It communicates with the brain through two arrays of electrodes, placed on either side of the damaged area. One records the electrical activity coming in from the rest of the brain, while the other sends appropriate electrical instructions back out to the brain. The hippocampus can be thought of as a series of similar neural circuits that work in parallel, says Berger, so it should be possible to bypass the damaged region entirely.

The hippocampus has a similar structure in most mammals, says the researchers, so little will have to be changed to adapt the technology for people. But before human trials begin, the team will have to prove unequivocally that the prosthesis is safe.