An international team of scientists report that a wireless brain implant that stimulates electrodes in the leg by recreating signals recorded from the brain has enabled monkeys with spinal-cord injuries to walk.

The research, conducted in Beijing, China by a collaboration led by Ecole Polytechnique Federale Lausanne (EPFL) in Switzerland, together with Brown University, Medtronic and Fraunhofer ICT-IMM in Germany, appears to be one the first times wireless brain-control was established to restore walking in an animal. The project is part of an effort to develop implantable systems which could restore volitional movement to paralyzed people.

Components of the brain-spine interface.Researchers first mapped how electric signals are sent from the brain to leg muscles in healthy monkeys, walking on a treadmill, and examined the lower spine, where electric signals from the brain arrive before being transmitted to muscles in the legs. Then they recreated those signals in monkeys with severed spinal cords, focusing on particular key points in the lower part of the spine.

Microelectrode arrays implanted in the brain of paralyzed monkeys picked up and decoded the signals that had earlier been associated with leg movement. Those signals were sent wirelessly to devices that generate electric pulses in the lower spine, which triggered muscles in the monkeys' legs into motion (see video).

With the system turned on, the animals began spontaneously moving their legs while walking on a treadmill. Kinematic comparisons with healthy controls showed that the lesioned macaques, with the aid of brain-controlled stimulation, were able to produce nearly normal locomotor patterns.

While the system used in this study successfully relayed signals from the brain to the spine, it lacks the ability to return sensory information to the brain. The team was also unable to test how much pressure the animals were able to apply to the affected leg.