A Nervous Proposition

Our brains constantly and subconsciously send commands to which our bodies react almost simultaneously. And the internal communications network that accomplishes this miraculous feat is the nervous system. But for many stroke patients, a portion of the nerve network crashes, and that often results in paralysis. Researchers have for years tried using artificial stimulation to sidestep the damaged portion of the system, with little success. Nerves don't appreciate being tampered with. But now scientists at Aalborg University in Denmark have developed electrodes that allow for artificial neuro-stimulation, a breakthrough that may help many stroke patients overcome paralysis.

Aalborg's initial technology is an implant — like a pacemaker — that "stimulates the nerve to mimic natural movement," explains Thomas Sinkjaer, the professor who is heading the research. It will benefit patients who sustained so much damage that they are beyond rehabilitation therapies and would otherwise remain paralyzed.

Artificially stimulating nerves to perform even simple tasks is a challenge. Even a routine movement, like picking up a paper coffee cup, requires a complex set of instructions to the hand to determine, among other things, how much pressure is needed. Too little pressure, and the cup is dropped; too much, and it's crushed. But the sensors Sinkjaer's team developed can pick up nerve impulses sent to and from the brain to determine how much stimulation is needed to control grasp.

Another hurdle they had to overcome was the subconscious element of movement. How often are we aware that our brain is telling a hand to pick up a cup, scratch an itch, or manipulate a PC mouse? The prototype developed in the lab uses subtle head movements to activate the stimulators to, say, open or close a hand. But Sinkjaer says future versions will actually be able to scan and pick up subconscious commands from the brain within the nerve traffic. "But that is some distance out in the future."

Efforts to connect electrodes directly to nerves failed because they're rejected by neuro-tissue. "Interfering with the nervous system is very, very difficult," Sinkjaer says. To avoid that problem, his team developed electrodes that wrap around the nerves. "The nerves tolerate this," he says, but the resolution is not is great. He is confident, however, of eventually devising electrodes that nerves will grow into, creating better, direct connections.

For those stroke patients who can respond to therapies to regain natural control of their limbs, Sinkjaer is also working on a "brain train" stimulator that could speed the rehabilitation process. As the stimulator causes, say, an arm to rise, patients learn to follow the movement and retrain their brains to regain control of that gesture.

The implant technology has been licensed to Neurodan, an Aalborg company, and the first commercial product could be ready within a year, Sinkjaer says. A therapeutic device could be available within five years. Sinkjaer's newfound ability to tap into and decipher nerve impulses may reap other benefits, as well. Neuro-stimulators may eventually be used in prosthetic devices for amputees that react to commands directly from the brain.