At first glance the toy car zipping around Jeff Bloomquist's lab looks ordinary enough. But closer scrutiny reveals something odd. Lashed to a small boom that juts like a bowsprit from the front of the car is a cockroach. Bloomquist, an insect neurophysiologist at Virginia Tech, and Steven Bathiche, now a bioengineering graduate student at the University of Washington, are trying to harness the neuromuscular reactions of insects to control model cars. To what end? They hope to scale up the concept and develop a wheelchair that handicapped people could control with the electrical impulses generated by, say, the twitch of a facial muscle.
In their experiment, the researchers attach an electrode to the muscles the cockroach uses for flying. When the researchers blow air on the cockroach, the slight breeze and the insect's unsupported feet make the roach think it's aloft, so it starts moving its wing muscles. The electrode reads the electric signals the muscles make when they contract and sends them to a microprocessor on the car, which starts the motor. "The first time we made it work, the thing just went blasting down the hall," says Bloomquist. "The movement generates a breeze that reinforces the flight behavior, so it flies for a long time."
However, the cockroach-driven model has some drawbacks. "Cockroaches only fly short hops, and they don't steer that well," says Bathiche. So he now uses hawkmoths. "They are much more elegant fliers. They are one of the fastest insects in the world, and the thing that's really nice is when they want to turn, they lean in the opposite direction."
Bathiche made a harness that measures how the moth shifts its weight when turning and uses that signal to steer the car in the direction the moth wants to go. He has also fine-tuned the microprocessor so that the speed of the car varies. When the moth wants to speed up, it beats its wings faster; Bathiche's microprocessor detects the change and accelerates the car.
Bloomquist and Bathiche don't anticipate any significant problems in developing a muscle-controlled wheelchair. Human muscles are so big that they generate relatively large electric signals just from tensing slightly, says Bloomquist. In fact, the researchers say human trials probably won't require any more intermediate steps. "Feedback from the experimentee is going to be very important to set up a system like this," says Bathiche. "You can't talk to a paraplegic dog and ask if it works."