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Intelligent Machines

Slow Motion

A 1985 essay saw hope—and immense challenges—for systems that might allow paralyzed people to walk again.

  • February 18, 2014

Excerpted from “Helping Paraplegics Walk: Looking Beyond the Media Blitz,” by Howard Jay Chizeck, from the July 1985 issue of Technology Review.

In the last two decades, researchers have begun to stimulate paralyzed limbs electrically in an effort to restore function to paralyzed muscles. At least 12 research centers worldwide are investigating ways to apply, control, and coordinate such electrical stimulation, which is called functional neuromuscular stimulation. The results so far are promising: these experimental techniques have enabled a small, carefully selected group of paraplegic patients to walk hundreds of meters in the laboratory, using walkers for support.

In all vertebrate animals, motion is accomplished when muscles contract. The muscles are turned on electrically by signals carried by nerves, which form the wiring of the motor-control system. When the spinal cord is injured, motor-control signals from the brain to the muscles may be disconnected.

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The hope is to develop ‘neural prosthetic’ devices that can at least partially replace the function of the injured spinal cord.

The problem, however, is much more difficult than simply restoring signal transmission. Researchers must find some way of approximating the extraordinarily complex system for human motor control.

All existing neural prostheses work in similar ways. First, the patient generates commands either by making a physical movement or by turning a switch off or on. In some experimental systems, quadriplegics move their shoulder a certain way and a transducer mounted on the shoulder translates that movement into an electrical signal.

This signal then prompts muscles in the hand to contract a certain way. If the person pulls his shoulder back, for instance, his finger and thumb open and extend. In this way, a sequence of different shoulder movements can enable a quadriplegic to grasp and pick up a coffee cup.

In most experimental systems for paraplegics, the patient generates binary (on-off) signals using simple hand switches. The signals are sent to an electronic ‘stimulator,’ which uses this information to generate one electrical signal for each electrode. The electrodes carry these signals into the body, where they stimulate specific muscles. When all these muscles are stimulated in the proper sequence, acts such as walking or grasping an object—which so many of us take for granted—can be achieved.

The future of efforts to restore muscle function to disabled individuals through the use of electrical stimulation is promising. However, multidisciplinary teams of scientists, engineers, and health-care professionals will have to work long and hard to solve difficult technical problems before these devices become widely available. This research should not be pressured by premature and exaggerated accounts of success in the popular press, which may raise false hopes among patients and damage the credibility of investigators in the field.”

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