You may not think you have much in common with the lamprey eel, arguably the most primitive vertebrate, but the truth is, it’s got your back. Though the bones are different, the neural components of a lamprey eel’s spinal cord are much the same as humans’ but are simpler and easier to understand. By studying these animals, researchers from Johns Hopkins University and the University of Maryland hope to develop an implantable chip, replicating spinal-cord nerves, which could someday help people with spinal-cord injuries walk again.
When a person has a spinal-cord injury, the nerve bundles below the spinal column are generally still intact. The problem is that the brain can no longer send them instructions to fire or stop firing. The implantable chip being developed?measuring just 4 mm by 4 mm, and requiring just 10 to 20 microwatts of power?attempts to control them in place of the brain. “We let the spinal cord do its thing, we just control circuits that make that spinal cord do its thing,” says lead researcher Ralph Etienne-Cummings, an associate professor of electrical and computer engineering at Johns Hopkins.
Etienne-Cummings says designing the chip isn’t the hard part of the project; understanding and controlling the lamprey eel’s spinal cord is. He is working with University of Maryland biology professor Avis H. Cohen, a neuromorphic engineer who specializing in systems and motor control. Cohen has been studying spinal-cord regeneration in lampreys since 1977.
“Designing the chip is not that difficult,” Etienne-Cummings says. “It is a very standard technology that has been around for a long time, used to develop microprocessors. The technical difficulty is in understanding the spinal cord, where to stimulate it, and so on. If you understand the organism, then you can replicate that in some sense in silicon.”
The chip contains a number of silicon circuits that behave the same way neurons do. For now, these neurons are connected together and integrated into motors that control walking in robots. Iguana Robotics, Inc. president M. Anthony Lewis is collaborating on this part of the project. The researchers will continue to study lamprey eels until they have enough detail to make a good model of its neurons on the silicon chip.
The next step in the process will be to implant the chip in rodents with spinal-cord injuries. Once the researchers successfully stimulate rodents’ spinal cords, they can begin to test the chip in humans. If the project succeeds, they anticipate starting human testing in about 10 years. It will be used to treat people with thoracic lesions (who still have control of their upper bodies) rather than treating those with cervical lesions, the kind the late Christopher Reeve had, which are higher up on the spinal cord and thus impair more of the body.
The chip-building aspect of the project is nothing new, Etienne-Cummings says, but his research team has taken it a step further. “People have implemented silicon neurons before,” he says. “The first report was back in the early 1990s. The aspect that’s new is we put together networks of these neurons and create signals for locomotary control.”
Some other treatments are being developed to treat spinal-cord injuries as well, and the project researchers say these varying approaches can complement each other. Functional electrostimulation involves electronic stimulators that act in lieu of the spinal cord, activating nerves so that muscles contract at the appropriate location. Stem cell-based regeneration, for which the research is still in a very early stage, attempts to regrow the actual nerve that has been cut.
Though much progress has been made, the researchers have a long way to go. The project team says they believe lamprey research indicates that other treatments, such as regeneration, will not be sufficient by themselves. Their implantable chip is intended to work with other methods.
“Lampreys automatically regenerate,” Etienne-Cummings says. “If you cut their spinal cord and put it back together, it will regrow eventually. However, when you do that, 75 percent of the time their swimming will not be back to normal. That’s why we think electrostimulation will have to complement regeneration to make things really work.”
By Natalie Goel