Designing Body Machine Interfaces
Posted by keelynet on June 6, 2009
Fascinating concept about central pattern generators!
“Ralph Etienne-Cummings studies animals in order to make devices that could one day help paraplegics walk, the armless feel and grasp, and machines see and fly like insects. A full professor at the age of 42, Etienne-Cummings enjoys a reputation internationally as a leading researcher in biomorphics, the engineering field that uses biologically inspired principles to make prosthetic limbs, robots, and other devices. His niche is neuromorphics, the study of how animals’ muscle control and sensory systems work so engineers can model them in silicon — or, put another way, jam-pack integrated circuits into microchips that can perform the same functions as nerve cells. When a person’s spinal cord is severed, signals from the brain can’t reach regions below the break. People who have a lower-spine injury also lose the ability of nerves in their legs to “talk” to each other, making the coordination necessary for walking impossible. Etienne-Cummings has sought to replicate the nerves that fire when a person walks — bundles of so-called controller nerves that create central pattern generators, or CPGs. In a healthy person, the generators feed signals into nerve cells in the spine — cells that remain even after a spine injury — and then respond to the output. The nerve cells learn to balance and coordinate the inputs and outputs in the proper sequence for locomotion. Etienne-Cummings challenged himself to come up with a way to tap this natural process to get paralyzed people moving again. Scientists at Case Western Reserve University, in Cleveland, have implanted nerve-like wires in paraplegics, who control the wires using a computerized box attached to their belts. This “functional electro-stimulation” model can get people walking by pushing buttons to lift or lower their legs. While hailed as a step forward for science and for patients, functional electro-stimulation also takes a step back: Patients tire quickly because the method moves muscle fibers in the opposite order than nature does. In essence, the machine works against the body as much as it does with it, tiring muscles that have been programmed by nature to respond differently. Another drawback: Patients must undergo extensive surgery to implant the wires. The technique Etienne-Cummings and others are developing, called intro-spinal stimulation, will fire nerves to move muscle fibers in the order nature intended, and it won’t require wire implants or an external controller. A better idea, but one that still needs some bugs worked out. Walking requires constant, simultaneous computations, coordinated movements, and feedback to the brain. Etienne-Cummings and crew must invent a CPG that does all that.” – Source
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