A MAN paralysed from the neck down by knife injuries sustained five years ago can now check his email, control a robot arm and even play computer games using the power of thought alone. Matt Nagle鈥檚 extraordinary abilities first grabbed the headlines in March 2005. Now details of the technology that lets him perform these and other tasks are published in Nature this week (vol 442, p 164).
Electrodes implanted in Nagle鈥檚 brain measure the neural signals generated when he concentrates on trying to move one of his paralysed limbs. Software trained to recognise different patterns of neural activity then translates the attempted gesture into the movement of an on-screen cursor or a robotic arm at Nagle鈥檚 side. 鈥淭he fundamental findings are that you can record activity from the brain years after injury, that thinking about movement is sufficient to activate the brain, and that we can decode the signal,鈥� says John Donoghue of Brown University in New York, who led the work.
Although Nagle鈥檚 achievement is truly remarkable and offers hope to many disabled patients, to get to this stage he has undergone risky surgery. Surgeons drilled a hole in his skull and inserted a pill-sized chip covered with 96 protruding electrodes into his motor cortex, an area at the centre of his brain that normally controls bodily movement. The operation carries the risk of infection and brain damage, an especially chilling prospect for someone already quadraplegic.
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The implant also has its limitations. Its electrodes can only sample a fraction of the relevant brain activity, and although Donoghue鈥檚 team is developing software to improve its accuracy, for the moment the signal can be patchy. This causes the cursor or robotic arm Nagle is controlling to wobble, and can make even simple tasks like checking email frustrating.
Less risky brain-computer interfaces exist, but at the cost of offering even less control. A group led by Benjamin Blankertz at the Fraunhofer Institute in Berlin, Germany, has developed a system that measures electrical activity via a skullcap lined with electrodes. While this lets users type at a speed of eight characters a minute, it cannot perform more complex tasks like manipulating a robotic arm.
With any such system one of the key issues is how fast thought can be translated into action. Fortunately, dramatic progress is being made in this area. In the same issue of Nature (p 195), Krishna Shenoy and colleagues at Stanford University in California report a way to dramatically boost the efficiency of brain implants in monkeys. Using software that predicts the monkey鈥檚 intention from only the first few bursts of neural activity, the animals were able to perform tasks at four times their normal speed 鈥� a rate roughly equivalent to a person typing out 15 words per minute.
If the same techniques work in people, Donoghue鈥檚 ambitious approach may yet be perfected. Working with researchers at Case Western Reserve University in Cleveland, Ohio, he ultimately hopes to enable quadraplegics to control their own limbs via electrical stimulation of their muscles. This could let Nagle and many others perform even more amazing feats of mind over matter.
