Bionic brain chips could overcome paralysis

A MONKEY sits on a bench, wires running from its head and wrist into a small box of electronics. At first the wrist lies limp, but within 10 minutes the monkey begins to flex its muscles and move its hand from side to side. The movements are clumsy, but they are enough to justify a rewarding slug of juice. After all, it shouldn't be able to move its wrist at all.

A nerve connection in the monkey's upper arm had previously been blocked with an anaesthetic that prevented signals travelling from its brain to its wrist, leaving the muscles temporarily paralysed. The monkey was only able to move its arm because the wires and the black box bypassed the broken link.

The monkey was in Eberhard Fetz's lab at the University of Washington in Seattle. The experiment, performed last year, was the first demonstration of a new treatment that might one day cure paralysis, which is typically caused by a broken connection in the spinal cord. Though much work has focused on using stem cells to regrow damaged nerve fibres, some researchers believe that an electronic bypass like this is equally viable.

The idea is to implant electronic chips in the relevant regions of the brain to record neural activity. Then a decoder deciphers the neural chatter, often from thousands of neurons, to figure out what the brain wants the body to do. These messages must then be relayed - ideally wirelessly - to electrodes that deliver a pulse of electricity to stimulate the muscles into action. Such "brain chips" are already restoring hearing to the deaf and vision to the blind, and helping to stave off epileptic fits, so the idea isn't as far-fetched as it might sound (see "Bionic medicine").

Every step of progress in tackling paralysis has been hard won. One of the early demonstrations that it may be possible emerged in 2003, when Josť Carmena, then at Duke University in Durham, North Carolina, successfully created an interface between brain and machine that allowed his lab monkeys to play a computer game using only their minds.

To gain a juice reward, the monkeys had to move a cursor - initially with a joystick - to hit a target on the computer screen. Beforehand, Carmena and his colleagues had implanted several chips throughout the parietal and frontal lobes of the monkeys' brains - regions known to plan and control movement. Each chip held up to 64 electrodes, which recorded the firing of the surrounding neurons as the monkeys manipulated the joystick.

Once the system had successfully decoded the chatter from the monkeys' neurons, the program stopped responding to the joystick's movement altogether and relied solely on the monkeys' thoughts to control the cursor. Eventually even the animals worked this out and stopped holding the joysticks as they completed the task (PLoS Biology, vol 1, p 42).

Manipulating a cursor on a computer screen is one thing, but whether such brain chips could translate the more complicated tasks of daily life remained an open question until 2004, when John Donoghue and colleagues from Cyberkinetics in Providence, Rhode Island, implanted a 100-electrode chip in the brain of a 25-year-old man known as MN, who had been left paralysed from the neck down by a knife wound.

Over the subsequent nine months, MN successfully used this BrainGate chip to open emails, operate a television and even control a robotic arm (Nature, vol 442, p 164). It was a promising step, but the technology was far from perfect. "Although BrainGate1 worked well in many ways, at times the control was not satisfactory," says Donoghue. And by the end of the trial, fluids from the brain had degraded the chip. The team are now solving these problems, and earlier this year announced the start of a clinical trial for an improved version of the chip.

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