In a collaboration that blends biology and robotics,
researchers at Johns Hopkins and the University of Maryland
are unraveling the circuitry in an eel's spinal cord to
help develop a microchip implant that may someday help
paralyzed people walk again.
After a spinal cord injury, many patients are unable
to move because the brain is cut off from nerve control
centers called central pattern generators, which are
believed to be located in the lower back. The two-school
research team's goal is to make a device that could mimic
the signals sent by the brain and coax these nerve centers
into sending "walking" instructions to muscles in a
"This is a challenging, long-term project, but we
believe it has a good chance to succeed," said Ralph
Etienne-Cummings, an electronics and robotics expert who is
lead researcher on the project at Johns Hopkins. "Our first
step is to learn how the brain transmits electrical
messages along the spinal cord that tell the legs what to
do. Then, we want to make microchips that replicate this
process. We've started by modeling the way swimming signals
move along the spinal cord of a lamprey eel."
Etienne-Cummings, an associate professor in the
Department of Electrical and Computer Engineering,
specializes in designing robotic devices that operate in
ways that resemble those found in biological organisms. In
the spinal cord project, he is working with Avis H. Cohen,
who has spent many years studying the lamprey's nervous
system and how it directs swimming. Cohen is a professor in
the Department of Biology, Neuroscience and Cognitive
Science at the University of Maryland, College Park.
"Even though the lamprey is a very primitive
vertebrate, we and others have shown that it's remarkably
like humans in the ways it makes and controls its
locomotion," Cohen said. "But unlike that of humans, the
lamprey's nervous system is remarkably easy to study."
The recent death of actor and research advocate
Christopher Reeve has increased the public's awareness of
efforts to help people with spinal cord injuries. The team
led by Etienne-Cummings and Cohen has already published a
paper describing the use of a microchip version of a
biological central pattern generator to produce a lifelike
gait in a robotic leg. In this project, funded by the U.S.
Office of Naval Research, the university researchers
collaborated with M. Anthony Lewis of Iguana Robotics.
The researchers are now moving to expand their project
by developing a neuroprosthetic implant that would connect
to human central pattern generators to restore locomotion
in patients with spinal cord injuries.
A first step: microchips,
foreground, being used to guide robotic legs.
PHOTO BY HPS/WILL KIRK
The lamprey is an ideal starting point,
Etienne-Cummings said, because the eel's spinal cord can be
removed and kept alive in a lab solution. By adding
chemicals, the eel's excised spinal column can be
stimulated to produce the pattern of nerve signals seen
when a live eel is swimming. "My collaboration with
Professor Cohen began when we tried to model the lamprey's
spinal cord circuits on a silicon microchip,"
Etienne-Cummings said. "That provided us with a more
natural way to control robotic limbs. But it also showed us
a possible way to interface electronically with human
To restore movement in patients with spinal cord
injuries, other researchers are trying to regrow severed
nerves or directly stimulate the muscles in paralyzed
limbs. Etienne-Cummings and Cohen are pursuing a different
but possibly complementary approach. They believe that even
when the central pattern generators that guide movement
from the lower back are cut off from the brain, they remain
A properly designed implant, they believe, could act
in place of the brain and direct these dormant control
centers to send the same kind of locomotion signals they
did before the spinal cord was injured. "We want to take
advantage of circuits that already exist in the body,"
Etienne-Cummings said. "Instead of stimulating the leg
muscles directly, we want to go to the spinal cord and
stimulate the nerves that control the muscles in the
He envisions the device that would accomplish this as
one that would contain mixed-signal (analog and digital)
very large-scale integrated microchips. The device would be
small and relatively inexpensive, running on a low-power
Etienne-Cummings cautioned, however, that much work
lies ahead. After the researchers conclude their studies on
lampreys, they must determine whether the results can be
transferred to small mammals, such as rats. Routine use in
humans could be at least 10 years away.
The continuing research has been supported by funding
from the Office of Naval Research, the National Science
Foundation and the National Institutes of Health.