Tiny Electrodes for the Brain

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Beyond use in deep brain stimulation, Llinas says his electrodes could detect signals, say, in the area of a person's brain responsible for directing arm movement. These signals could then be used to drive a robotic arm, restoring some abilities to people paralyzed by brain and spinal-cord injuries. Llinas says the first application of the nanowire electrodes may be to route nerve impulses around damaged areas of the spinal cord, either to other nerves or directly to muscles, possibly restoring function to paralyzed limbs.

The nano electrodes could also play a role in improving the cochlear implants used to restore hearing. Because the electrodes are so small, it could be possible to increase the number of electrodes used in a cochlear implant, "to stimulate a broader region and give more color to sound," says Patrick Anquetil, a mechanical engineering postdoctoral fellow at MIT and one of the researchers on the project. He says the first commercial uses of the nanowire electrodes are probably still five years away.

In the future, the researchers plan to build steerable electrodes. To do this, they will use a polymer that contracts in response to electricity. A bundle of such nanowires could be directed, by causing selected nanowires to contract.

The researchers think that, eventually, the bundle of nanowires could partly steer itself. Anquetil says they have made polymers that act as pressure sensors, and they see the possibility of using semiconducting polymers as the basis for simple electric switches. "One thing that really excites us about this is, in principle, there's no reason why, with the same material, you cannot build a whole system in which you have contraction, measurement, sensing, and computation."

While the first bundles would use relatively few electrodes, thousands could eventually be grouped together to form a package no wider than the 1-2 millimeter probes Llinas says are used today in the brain. Once near the targeted area, the nanowires would be allowed to separate. The wires would then spread out, pushed into a branching network of capillaries. This would allow researchers to monitor and deliver impulses to individual neurons deep inside the brain in a distributed area, an ability that could prove a boon to brain researchers now limited to using relatively small arrays of electrodes.