Monday, September 12, 2005

Silicon chip for the brain

Dr. K. Rohiniprasad

Human brain is frequently compared to a computer and chess grandmasters pitting their talents against computers make occasional headlines. On another front, advances in surgery have resulted in the use of artificial hip joints, implanted pacemakers, heart valves and so forth. Recent research is proving that the human brain is no longer out of bounds for such experiments. Theodore Berger, from the University of Southern California in Los Angeles and his colleagues have developed a “brain chip”, a silicon chip that could be used to replace the hippocampus. Hippocampus is a structure in the limbic system of the brain, which is associated with short term memory. A major component of our ability to remember and recall is localised in the hippocampus at the base of the human brain, close to the junction with the spinal cord. It "encodes" experiences so they can be stored as long-term memories in another part of the brain. Injuries in that area cause profound memory impairment.

The "brain chip" will initially be tested on the brains of rats. It is hoped that the present work could replace the "memory centre" in patients affected by strokes, epilepsy or Alzheimer's disease. If the tests are satisfactory, the artificial hippocampus will be tested in live rats within six months and then monkeys trained to carry out memory tasks. Human trials will be taken up only if the chip proves to be safe. Current devices, such as cochlear implants, only stimulate brain activity. If successful, the silicon chip - the first brain prosthesis - will be able to replace damaged brain tissue.

The researchers have spent 10 years developing the artificial hippocampus. At the moment scientists simply copied the behaviour of hippocampus since they do not know how exactly it works. In this effort slices of rat hippocampus were stimulated with electrical signals millions of times, to understand which input produced a corresponding output. The researchers were able to devise a mathematical model of a whole hippocampus by putting together the information obtained from each slide. The model was then programmed on to a chip, which would be placed on a patient's skull, rather than inside the brain. The chip would communicate with the brain via two arrays of electrodes, placed on either side of the damaged portion. One electrode would record the electrical activity coming from the rest of the brain, while the other would send out the necessary instructions back to the brain. Since the hippocampus acts as a series of similar circuits that work in parallel, it should be possible to bypass the damaged area. More tests will be done on the slices of rat brains kept alive in cerebrospinal fluid.

Scientists say this is a test case. "If you can't do it with the hippocampus you can't do it with anything."