World's first brain prosthesis revealed

The world's first brain prosthesis - an artificial hippocampus - is about to be tested in California.

World's first brain prosthesis revealed
19:00 12 March 03
Duncan Graham-Rowe

The world's first brain prosthesis - an artificial hippocampus - is
about to be tested in California. Unlike devices like cochlear
implants, which merely stimulate brain activity, this silicon chip
implant will perform the same processes as the damaged part of the
brain it is replacing.

The prosthesis will first be tested on tissue from rats' brains, and
then on live animals. If all goes well, it will then be tested as a
way to help people who have suffered brain damage due to stroke,
epilepsy or Alzheimer's disease.

Any device that mimics the brain clearly 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, Missouri.

The researchers developing the brain prosthesis see it as a test
case. "If you can't do it with the hippocampus you can't do it with
anything," says team leader Theodore Berger of the University of
Southern California in Los Angeles. The hippocampus is the most
ordered and structured part of the brain, and one of the most
studied. Importantly, it is also relatively easy to test its function.

The job of the hippocampus appears to be to "encode" experiences so
they can be stored as long-term memories elsewhere in the brain. "If
you lose your hippocampus you only lose the ability to store new
memories," says Berger. 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.

Model, build, interface

The inventors of the prosthesis had to overcome three major
hurdles. They had to devise a mathematical model of how the
hippocampus performs under all possible conditions, build that model
into a silicon chip, and then interface the chip with the brain.

No one understands how the hippocampus encodes information. 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 (see graphic).

Memory tasks

Berger and his team have taken nearly 10 years to develop the
chip. They are about to test it on slices of rat brain kept alive in
cerebrospinal fluid, they will tell a neural engineering conference in
Capri, Italy, next week.

"It's a very important step because it's the first time we have put
all the pieces together," he says. The work was funded by the US
National Science Foundation, Office of Naval Research and Defense
Advanced Research Projects Agency.

If it works, the team will test the prosthesis in live rats within six
months, and then in monkeys trained to carry out memory tasks. The
researchers will stop part of the monkey's hippocampus working and
bypass it with the chip. "The real proof will be if the animal's
behaviour changes or is maintained," says Sam Deadwyler of Wake Forest
University in Winston-Salem, North Carolina, who will conduct the
animal trials.

The hippocampus has a similar structure in most mammals, says
Deadwyler, 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.

Collateral damage

One drawback is that it will inevitably bypass some healthy brain
tissue. But this should not affect the patient's memories, says
Berger. "It would be no different from removing brain tumours," where
there is always some collateral damage, says Bernard Williams, a
philosopher at Britain's University of Oxford, who is an expert in
personal identity.

Anderson points out that it will take time for people to accept the
technology. "Initially people thought heart transplants were an
abomination because they assumed that having the heart you were born
with was an important part of who you are."

While trials on monkeys will tell us a lot about the prosthesis's
performance, there are some questions that will not be answered. For
example, it is unclear whether we have any control over what we
remember. If we do, would brain implants of the future force some
people to remember things they would rather forget?

The ethical consequences of that would be serious. "Forgetting is the
most beneficial process we possess," Williams says. It enables us to
deal with painful situations without actually reliving them.

Another ethical conundrum concerns consent to being given the
prosthesis, says Anderson. The people most in need of it will be those
with a damaged hippocampus and a reduced ability to form new
memories. "If someone can't form new memories, then to what extent can
they give consent to have this implant?"


add a comment on this article