Nerves of silicon: Neural chips eyed for brain repair

March 17, 2003 2:32pm

ELECTRONIC ENGINEERING TIMES, Page 1, March 17, 2003

San Mateo, Calif. - Researchers at the crossroads of medicine and
electronics are developing implantable silicon neurons that one day
could carry out the functions of a part of the brain that has been
damaged by stroke, epilepsy or Alzheimer's disease.

The use of neural chips to replace brain functions is "mostly in an
animal-research phase now. Work in humans could be five or 10 years
away," said Metin Akay, an associate professor of psychology and
brain sciences at Dartmouth College and chairman of the first
international conference on neural engineering, to be held this week
in Capri, Italy. But some of the roughly 180 papers to be presented
in Capri give tantalizing hints of the potential of this emerging
technology.

"We are trying to figure out how to develop a prosthetic that allows
one part of the brain to talk to another," said Theodore Berger,
director of the center for neural engineering at the University of
Southern California and one of the researchers at the forefront of
the implantable-neuron effort. "We've done all the pieces of the
problem and now we are trying to fit them together," said Berger, who
has prepared a paper on his work for the meeting.

Akay called the conference the first "to really unite rehabilitation
and computer scientists, electronics engineers and neural
scientists." Researchers from 30 countries will attend. "I hope it
will further stimulate research in the field," said Akay, who has
helped establish and promote the discipline of neural engineering. He
described it as "a new concept and a diverse field that spans
medicine, physics, computer science, electronics and more."

Applications for this combination of electronics and neural science
span neural computing, advanced robotics and improved drug sensors as
well as better fundamental knowledge of the brain. "We still do not
understand perhaps 80 percent of the functions of the brain," said
Akay.

Because the field is so new, it's tough to say exactly where it is
headed. "I can't tell what the real applications are yet, but it
could be important both for computing and medicine," said Peter
Fromherz, a professor of neurophysics at the Max Planck Institute for
Biochemistry (Munich, Germany), who will present a plenary paper on
his experiments growing neurons directly on a 2-D transistor array
from Infineon Technologies
(see http://www.biochem.mpg.de/mnphys/publications/02fro3/02fro3.pdf
).

At USC, meanwhile, Berger's team first stimulated a slice of a rat's
brain with a random-signal generator to determine its functional
patterns and develop mathematical models representing them. The group
then coded those models into an analog chip.

USC researchers have spent 10 years working largely with analog
devices because they found the continuous rate of discharging
capacitors was good for mimicking continuous neural functions. "But
if you are going to need tens or hundreds of thousands of neuron
models on a chip, analog capacitor models won't scale well," Berger
said.

"We're now looking at an SoC [system-on-chip] approach that mixes
digital and analog techniques," said John Granacki, director of the
advanced-systems division of USC's Information Science Institute. "We
are looking at digital blocks such as fixed-point arithmetic units
that can generate recursive Laguerre polynomials to provide universal
functions." These polynomials, he said, "are very compact and don't
require much addition, subtraction or multiplication to generate
functions. Meanwhile, simple analog circuits help indicate peaks for
neural signals."

The team's next-generation chip, a hybrid digital/analog device, will
use 130-nanometer process technology and could form the basis of what
researchers envision as a host of chips that run the gamut from fixed-
function to highly programmable parts. "We think we can create whole
families of devices that can do [neural] pattern matching," Granacki
said.

Wake Forest University (Winston-Salem, N.C.) is starting work with
Berger's team in a three-year program to integrate all their separate
research projects in an experiment on an intact rat brain. A future
project on a monkey could take five years, Berger said.

At the same time, Berger is in the middle of reviews to compete for a
National Research Foundation grant for a new center at USC devoted to
neural engineering. Besides the work on neural prosthetics, that
center would include two other testbeds.

One involves injectable neuromuscular stimulators that could operate
a paralyzed limb and be managed wirelessly through controls sewn on a
sleeve. A separate project, in conjunction with Johns Hopkins
University (Baltimore), is working on a silicon-based array of
photosensors made on a curved surface that could be fitted to the
back of a damaged human retina. Both projects are in clinical trials
and could see commercial results in five years, the scientists said.

Missing links
One of the toughest problems in neural prosthetics is how to connect
chips and real neurons. Today, many researchers are working on tiny
electrode arrays that link the two. However, once a device is
implanted the body develops so-called glial cells, defenses that
surround the foreign object and prevent neurons and electrodes from
making contact.

"We are working with chemists and materials scientists to figure out
how to coat interface devices with a biological or biological-like
material that will attract neurons," said Berger-perhaps something
sticky to which neurons would adhere. "It's a hard problem."

In Munich, the Max Planck team is taking a revolutionary approach:
interfacing the nerves and silicon directly. "I think we are the only
group doing this," Fromherz said.

Fromherz is at work on a six-month project to grow three or four
neurons on a 180 x 180-transistor array supplied by Infineon, after
having successfully grown a single neuron on the device. In a past
experiment, the researcher placed a brain slice from the hippocampus
of a monkey on a specially coated CMOS device in a Plexiglas
container with electrolyte at 37 degrees C. In a few days dead tissue
fell away and live nerve endings made contact with the chip.

"Sometimes the [nerve-silicon] coupling is good, other times it is
poor," Fromherz said. "We understand the physics, but in terms of the
engineering we have very little control. We have to improve both the
chips and the cells."

Solving the interface issue lies in letting the brain do much of the
work, said James Hickman, a surface chemist and assistant professor
in the Hybrid Neuronal Systems Lab at Clemson University (Clemson,
S.C.).

Hickman, who has successfully grown systems of neurons using
geometric queues, noted that in cochlear (inner-ear) implants, the
auditory nerve actually reconfigures itself to interpret the 10-
channel signal the implant emits. "Now we have to get more
sophisticated in the types of connections we make," he said. "We
would like to send out a signal that recruits the right nerves to the
right contacts. How you control that reconfiguration is the next big
step in neural prosthetics."

Developing a device that has both transistors for recording neural
data and capacitors for stimulating neurons is a next step for
Fromherz. "With brain slices we do not know yet how many [or how few]
nerves we can stimulate and record. We need to learn how many nerves
we need to precisely control [to get a desired result], and we are
just at the beginning of this learning."

Help for Parkinson's
The U.S. Food and Drug Administration has approved implantable
neurostimulators and drug pumps for the treatment of chronic pain,
spasticity and diabetes, according to a spokesman for Medtronic Inc.
(Minneapolis). A sponsor of the Capri conference, Medtronic says it
is already delivering benefits in neural engineering through its
Activa therapy, which uses an implantable neurostimulator, commonly
called a brain pacemaker, to treat symptoms of Parkinson's disease.
Surgeons implant a thin, insulated, coiled wire with four electrodes
at the tip, then thread an extension of that wire under the skin from
the head, down the neck and into the upper chest. That wire is
connected to the neurostimulator, a small, sealed patient-controlled
device that produces electrical pulses to stimulate the brain.

The Activa device was approved for use in Europe in 1998 and in the
United States last year. "I have interviewed some of these patients
and it is amazing to see them do simple things like drink a cup of
coffee or walk-things they cannot do without this device," said Akay
of Dartmouth.

http://www.eet.com

Copyright © 2003 CMP Media LLC

SOURCE: Hoover's Online
http://hoovnews.hoovers.com/fp.asp?layout=displaynews&doc_id=NR2003031
7350.1_bf45004e369770be

* * *

----------------------------------------------------------------------
To sign-off Parkinsn send a message to: mailto:[log in to unmask]
In the body of the message put: signoff parkinsn