by
Olga Deshchenko, DOTmed News Reporter | April 15, 2011
From the April 2011 issue of HealthCare Business News magazine
Vanderbilt University is one of the facilities working on the stimulation side of the initiative. E. Duco Jansen, a professor of biomedical engineering and neurosurgery with the university who’s working on the project, says that today’s prosthetics function with the help of an electrode that either sends or picks up signals from the nerves or muscles. Although this technology works fairly well, it has some fundamental limitations. “The main one is really one of spatial accuracy,” he says. “How accurately can you control that prosthetic device?”
For Vanderbilt’s portion of the research, Jansen’s team is using lasers to stimulate the nerves. The researchers are employing infrared lasers, which can effectively focus on even individual neurons. As tissue is exposed to the light, the neural tissue absorbs it, causing the nerves to fire an action potential. “That’s the currency that the nervous system talks in and so that way, we have a way to use light to encode action potentials in the nervous system with high precision and code those back into or pick them up from the nervous system and put them in the robotic arm,” says Jansen. “It’s really the area of building better neural interfaces and in our case, we’re pursuing laser technology to do that.”
Jansen says the idea for using beams of light for neural stimulation was an “accidental discovery.” Several years ago, a neurosurgeon from Vanderbilt’s medical school sought help from the biomedical engineering department. During surgical procedures where clinicians insert electrodes into the brain for say, controlling Parkinson’s disease or epilepsy, surgeons can spend hours probing different parts of the brain for activity in order to determine exactly where the electrodes should be placed. The procedure is extremely tedious, burdensome and expensive. The surgeon wanted to know if there was a way to ease the process by optically “seeing” electrical activity in the brain.
While researching the neurosurgeon’s problem, the team came up with its own question. “If you could see electrical activity in the brain with light, why can’t we turn it around and induce electrical activity in the brain with light?” asks Jansen.
For starters, they exposed a nerve in a frog’s leg to laser pulses, hypothesizing a set of laser parameters they thought might work. When they focused the pulses directly on the leg’s sciatic nerve, it contracted. “With every laser pulse, we saw a little twitch of a muscle in the frog leg,” says Jansen.
Still, it was possible they were stimulating a reflex arc, similar to what a physician does when tapping on a knee with a little rubber hammer. So they cut the connection between the nerve and the spinal cord. “And yet, when we put the laser on the nerve, we still saw the muscle twitches. That was direct evidence that we were inducing action potentials leading to motor responses in the frog leg,” says Jansen.
