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though, such as whether the communication can work in both direc- tions; that is, both from and to the brain, and whether the technique can be made fine-scaled enough to pick up signals from individual neurons. But the achievement of a noninvasive BMI would give a different meaning to bionic enhancements for civilians as well as sol- diers; instead of submitting to a serious surgical procedure, a person could freely add or remove neural prosthetics, such as auxiliary memory or communication devices.

Other researchers are working on truly radical methods to inter- face neurons with electronic devices. One pioneer, Peter Fromherz of the Max Planck Institute for Biochemistry in Martinsried, Germany, aims to connect individual nerve cells with transistors by creating a neuron on a chip.He sees possibilities for neural prostheses and BMI units, and for new ways to study the brain, but there are difficul- ties. Although both chips and neural structures encode information electrically, the mechanisms differ.A chip carries electricity by means of a lightning-fast flow of electrons in a solid, whereas a neural system carries electricity by sluggish electrochemical means involving the movement of ionscharged atomsin fluids. Hence the two systems operate at different time scales, nanoseconds for chips versus millisec- onds for neurons. Finding ways to interface the systems is one chal- lenge; ensuring that the silicon provides a proper base for nerve cells to grow and adhere is another.

Despite these challenges, Fromherz has created what might be called nanocyborgs, that is, prototypical neuronchip hybrids, which consist of neurons from rat brains, leeches, or snails specially grown atop silicon chips so that the neurons overlay the transistors etched into the chips. Fromherzs initial experiments show that the natural and the artificial systems indeed communicate directly; that is, electri- cal activity in the neuron causes activity in the chip, and vice versa. In a more complex demonstration, when two snail neurons were placed some distance apart on a silicon chip, the firing of one neuron in- duced the other to fire, although they were not linked by neuronal means but only through the silicon. Fromherz has also extended his technique to entire sections of a brain. In a structure consisting of a

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