A silicon chip with a lot of nerve.

The science fantasy of computers that send signals straight to a brain has taken a small step toward reality.

Peter Fromherz and Alfred Stett, physicists at the Max Planck Institute of Biochemistry in Munich, have made a silicon chip that can directly stimulate a nerve cell. Their so-called silicon-to-neuron junction, reported in the Aug. 21 Physical Review Letters, triggers a single nerve cell in a leech without killing the cell.

"It is possible now to interface individual neurons with silicon microstructures in both directions," they say, "from silicon to neuron, by stimulation of a [membrane] spot, and from neuron to silicon, using a metalfree field effect transistor."

In previous artificial nerve stimulators, metal leads tended to corrode and shed toxic by-products. In contrast, the silicon chip propagates a voltage pulse from a tiny spot on the cell membrane. This causes a buildup of positive charge that trips a neuronal impulse.

The new chip complements "neuron transistors" that receive ionic nerve impulses, transforming them into an electric impulse on a silicon chip. Together, the two microstructures offer the possibility of direct, two-way communication between a nervous system and machinery.

Still, employing the device for medical purposes--to control an artificial limb, for example--lies far in the distance, the scientists conclude. Exactly how practical it will prove, they say, "remains to be seen."