These initial experiments have been performed "off-line," meaning that brain activity was recorded and then fed into the system at a later time. But researchers are planning a live demonstration within the next six months. Monkeys implanted with an array of recording electrodes will be hooked up directly to a virtual version of a prosthetic arm, which is currently under development. Scientists will then determine how well these animals, which are trained to perform specific hand movements, can use their brain activity to control the virtual hand in real time.

While preliminary results are exciting, scientists have a long way to go before they can mimic the true dexterity of the hand. "Each finger has three or four degrees of freedom that need to be controlled: flexion and extension at each of three joints, as well as adduction and abduction," says Schieber. Added to that is the complexity of moving five individual fingers, sometimes in unison and sometimes independently.

Scientists don't yet know if the decoding system they have built will be able to execute unique actions--movements that were not a part of the original repertoire used to create the decoder. "In the long run, we want [the monkey] to be able to do anything he can think of in the moment," says Schieber. "But getting the decoding algorithm to generalize like that is another challenge."