BioEd Online

Five years ago, Matt Nagle was stabbed, leaving him paralysed in all four limbs. But since then, he has been able to use a modified computer to open e-mails, adjust the volume on his television, move a robotic arm and even play the computer game Pong. These powers came courtesy of a tiny square of electronic gadgetry implanted directly in his brain.

Nagle is a pioneer in the world of 'brain-computer interfaces'— the quest to design devices that can read people's minds, allowing them to control computers and robots simply by thinking about it. The neuroscientists and technicians leading this drive hope that, in just a few years, such devices could routinely and effectively be used by paralysed patients.

The device implanted into Nagle's brain, called the BrainGate, is an encouraging step on that journey. Created by neuroscientist John Donoghue of Brown University in Providence, Rhode Island, and developed by a Massachusetts-based start-up company called Cyberkinetics, it was hailed as a breakthrough in 2004 when Nagle first successfully used it (see ' Paralysed man sends e-mail by thought').

The BrainGate consists of 96 electrodes, implanted into a brain area called the motor cortex, the command centre for body movements. In many paralysed patients the nerve cells that issue these commands still function, even though the motor nerves do not respond.

Further trials on another paralysed volunteer also met with some success, although the device stopped functioning after 11 months, Donoghue's team reports in this week's Nature¹. The researchers are still investigating why this happened.

In or out

The BrainGate only makes possible a rudimentary range of movements, and it relies on an external box of wires to help interpret the brain's commands. Many paralysis patients are young, so using such a device for years or even decades would be impractical, given the risks of infection from connections running through the skin.

One alternative is to record brain activity from the outside, without surgery, using an electroencephalogram, or EEG (see ' Computer users move themselves with the mind'). Such external EEG devices are easy to build and test, and so have traditionally been used instead of implants. "The functionality that can be restored with an implanted device is at the moment not much superior to what can be done using much cheaper devices that do not require surgery of any kind," comments Francisco Sepulveda, who studies brain-computer interfaces at the University of Essex, UK.

But EEG systems are still frustratingly difficult to use, as external electrodes must make sense of a mishmash of electrical noise coming from the brain's millions of cells.

The challenge, therefore, is to develop a self-contained, implantable system that is sensitive and speedy enough to allow efficient communication that lasts a lifetime, says Krishna Shenoy of Stanford University in California, who has been working on ways to improve the BrainGate's performance2. "We want to achieve performance that will make it worth the surgical risk," he says.

Final destination

Shenoy and his colleagues implanted the BrainGate into rhesus monkeys to investigate how the system might be fine-tuned. By placing the device in a slightly different brain area, they sought to detect not just the intended direction of cursor movement on a screen, but rather the cursor's final destination, allowing the computer to jump straight there.

If this trick can be reproduced in humans, Shenoy and his team reckon that a BrainGate user might be able to 'type' at around 15 words per minute, by selecting letters on a display screen. Given the similarity between monkey and human brains, Shenoy says, "achieving that kind of rate could be extremely near-term."

In the meantime, Donoghue and his team are investigating whether the BrainGate could also help people paralysed by stroke, muscular dystrophy or motor neuron disease. Early results look promising.

But dreams of able-bodied people becoming bionic men and women might have to wait, he adds. "There's a long-term barrier to using it in able-bodied people because it would involve surgical implants," he explains. So while the technology would be a godsend for the paralysed, surgeons might be understandably reluctant to tinker with healthy brains.

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