Eavesdropping on the brains of monkeys with hand paralysis has helped restore near-normal function. The system could one day be trialled in people, too.
Currently available systems restore only basic hand control to people with damage to the spinal nerves that control the arms. The Freehand system, for example, uses sensors at the shoulder to detect shrugs. The sensors then trigger electric stimulators to activate hand muscles, allowing the person to clench or unclench their hand.
Lee Miller and his colleagues at Northwestern University, Chicago, think it is possible to fine-tune this control. They inserted 100 electrodes into the brains of two healthy monkeys to record the neural activity linked to different hand and arm muscle activity.
They then used an anaesthetic to paralyse the monkeys' wrist and hand muscles. By comparing subsequent brain activity with that recorded before paralysis, the team could predict the movement each monkey was attempting, and electronically trigger muscles in the monkey's hand to replicate the expected action. The animals regained enough control to successfully place a ball into a tube in 80 per cent of attempts
"If you walked into the room, you wouldn't realise the monkey is paralysed," says Miller. The system effectively mimics the way healthy people control their limbs, but because it bypasses the spinal cord, it could be useful for nerve-damaged individuals. "By going directly to the brain, we have potential access to a much richer set of control signals that represent the actual movement the patient is attempting to make."