Spawning sea lamprey (Petromyzon marinus),
Bond Brook, Augusta, Maine. June 2004.
Sea Lamprey May Offer Paralysis Cure in Humans
By Karen Lurie
www.wired.com
December 14, 2004
A man-machine interface inspired by the spinal cord of the eel-like sea
lamprey could someday enable paralyzed people to reliably control their
legs, possibly with a joystick at first, and eventually walk again.
After spinal cord injuries, many people become paralyzed because their
brains are cut off from central pattern generators, or CPGs, which are networks
of neurons in the spinal cord that are thought to produce an automatic walking
motion in toddlers or allow a chicken to run around without its head.
Ralph Etienne-Cummings, associate professor of electrical and computer
engineering at Johns Hopkins University, and Avis H. Cohen, a professor
in the department of Biology, Neuroscience and Cognitive Science and the
Institute for Systems Research at the University of Maryland, are blending
robotics and biology to develop a silicon implant that could someday tell
these nerve centers to send walking orders to a human patient's legs.
"When a human has a spinal cord injury where the top half of the body
can be controlled, but the bottom half cannot, the circuits that actually
control walking are still intact," said Etienne-Cummings. "We
just want to kick start those circuits and then fine-tune the behavior of
those circuits that already pre-exist in the spinal cord."
For help, they've turned to the lamprey, a creature with a removable spine
that can remain alive in a dish and be stimulated to move as if it's still
inside a swimming animal.
"The lamprey has a very simple -- but vertebrate -- nervous system,"
said Cohen. "It has no blood vessels in it, so it can stay alive outside
the body for a long time. The lamprey is also the most primitive vertebrate.
However, even with this simplicity, its spinal cord has all the characteristics
of a human spinal cord, but with many fewer neurons, and no bones. So, it's
easy to study."
The team, whose research is funded by the Office of Naval Research, the
National Science Foundation and the National Institutes of Health, has already
created a microchip version of an adaptive CPG that can control robotic
locomotion, in conjunction with Anthony Lewis of Iguana Robotics.
According to Etienne-Cummings, the team has developed a chip that contains
a silicon analog of the spinal circuits. Using the chip, which was modeled
on the lamprey spinal cord, researchers were able to control a biped robot.
Feedback from the joint angles and foot-falls of the robot were incorporated
to train the CPG to recognize the correct frequency and phase relationship
between limbs that is necessary for smooth and natural motions.
Without the sensory adaptation of the CPG circuits, the robot would have
exhibited a very significant limp or would not be able to walk at all, Etienne-Cummings
said.
Next up, said Cohen, is developing the hardware to control the spinal cord
on a moment-by-moment basis.
"We've been able to kind of impose our will onto the behavior of the
(lamprey's) spinal cord circuits," Etienne-Cummings said. The team
plans to work next with intact lampreys and then move to limbed animals.
The long-range goal, which could take at least a decade, is to develop
a neuroprosthetic implant for people that would connect to human CPGs and
induce and control walking. Etienne-Cummings pictures "an implant that
would essentially communicate directly with the circuits in the spinal cord."
He envisions an interface between the implant and the person controlling
it, possibly incorporating an input device like a joystick. A person with
an implant could push a button to move their legs forward or to turn.
All this from studying the lamprey, the jawless sea-dweller credited with
killing England's gluttonous King Henry I who found the fish irresistibly
tasty.
"A lot of the circuits that have been found in lampreys generalize
nicely to limbed animals such as mice and cats and humans," said Etienne-Cummings.
"So it's not a far-fetched concept to expect that the ideas we glean
from the lamprey will migrate upwards to limbed animals. Of course, we don't
expect it to be a simple migration."
Learn More About the Amazing Sea
Lamprey
of the Kennebec River
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