Originally Published MDDI February 2005

R&D DIGEST

Maria Fontanazza

Studying an eel's spinal cord could lead to the development of a neuroprosthetic device that controls walking. In theory, the device would directly interact with the nervous system and mimic brain signals that are sent to a person's legs.

Researchers at The Johns Hopkins University (Baltimore) and the University of Maryland (College Park, MD) are working with a lamprey eel's spinal cord to design a microchip implant that will form a functional network with the nervous system. The team, which also includes Anthony Lewis, founder of Iguana Robotics Inc. (Urbana, IL), is currently utilizing the lamprey eel to develop a stimulation and recording device. “We're using standard technology for implementing analog and digital circuits to produce stimulation signals that integrate with the eel's spinal cord,” explains Ralph Etienne-Cummings, associate professor of electrical and computer engineering at Johns Hopkins.

The process involves working out the algorithms that can control the spinal cord correctly. “We have to build devices that can make this happen autonomously, with some degree of control from the person,” says Etienne-Cummings, who is also the director of neuromorphic engineering at the University of Maryland.

Refining the device involves creating a smaller and extremely low-powered chip that won't need to be replaced often. It must also be compatible with neural circuitry. “We're still doing the basic scientific research at this point,” says Etienne-Cummings. “Once we know how to effectively control spinal neural circuits, we'll know the capabilities better.”

The device must also have more levels of control and chip action, because the signal coming out of it needs to be more complex, says Avis H. Cohen, a professor in the department of biology and Institute for Systems Research at the University of Maryland.

The researchers have three paths of ideas, says Etienne-Cummings. First, they need to create a robot with the natural qualities the researchers have gleaned from their study of the eel's spinal cord. This could produce an application for artificial limbs. Second, they must learn how to control the spinal cord in order to build a device that will allow a person to impose will onto an organ, similar to a remote control. Third, they will attempt to establish a connection to the part of the spinal cord that controls walking in limbed animals and, ultimately, in humans.

Cohen says the device is chiefly meant to control walking and would help patients with spinal cord injuries in the middle of the back, not the neck. The patient's upper body must also be intact and functional. She envisions a device that would turn on and control speed and uphill and downhill movement. It wouldn't need to control basic movements, such as reflexes, because those types of movements are programmed at birth.

The vertebral column of the lamprey is so primitive that it can be taken out of the animal and kept alive in a lab solution. “It also has all of the properties of a mammalian spinal cord,” says Cohen. “It's just a simpler, scaled-down version.” If the study is successful on the eel, researchers will move on to a rodent model to prove the device's use in a more complex spinal cord.

The research has been funded by the Office of Naval Research (Arlington, VA) and the National Institutes of Health.

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