By thought alone

2019-03-08 05:03:02

By Philip Cohen BIONIC rodents have brought “thought-controlled” prosthetic devices a step closer for people who are paralysed or have lost limbs. Neuroscientists in the US have trained rats to get a drink of water using a machine wired directly to their brains. People have already learnt to control computers using their brain waves, read by electrodes on the scalp, or implanted electrodes into which neurons were encouraged to grow (This Week, 16 January, p 4). Miguel Nicolelis of Duke University Medical Center in Durham, North Carolina, has also been working with brain implants. However, instead of relying on implants establishing random connections, he hoped to find the neurons involved in a specific task and link directly to these neurons. So Nicolelis teamed up with John Chapin and his colleagues at the MCP Hahnemann School of Medicine in Philadelphia, Pennsylvania. They implanted electrodes in the brains of six rats to eavesdrop on between 21 and 46 individual neurons. The animals had already been trained to operate a robotic arm to fetch themselves a drink of water. When they pressed a lever, the arm would pick up a drop of water from a dropper and give it to the rat when the lever was released. As the wired animals carried out this task, the researchers monitored the pattern in which the neurons fired and found a combined signal that preceded the movement of each rat’s paws when it managed to get a drink. Then they disconnected the robotic arm from the lever and connected it instead to each rat’s neurons, so their signals would control the arm directly. Even though the lever now had no effect, the animals continued to press it. In these early attempts, two of the animals slaked their thirst every time they performed the proper movements. Two other rats succeeded more than three-quarters of the time. The last two were able to trigger the robot 67 and 54 per cent of the time. But as this class in mind control continued, something remarkable happened. The circuit that moved the arm—which also received and interpreted the neuronal signals—operated so quickly that the arm began to move before the rats could push the lever. And the animals soon figured this out. After a dozen tries or so, they stopped depressing the lever fully. In fact, sometimes the animals received their wet reward without pushing the lever, or even moving a paw (Nature Neuroscience, vol 2, p 664). “It’s like the rat is just having a mental image of the motion, if a rat can do that,” says Nicolelis. “It’s a practical demonstration of how this prosthetic technology can work in real time,” says neuroscientist Eberhard Fetz of the University of Washington School of Medicine in Seattle, Washington. However, he cautions that Nicolelis and his colleagues are using neurons to control a device that is far simpler than prosthetic limbs for people would have to be. Nicolelis and Chapin admit that there is plenty of work to be done. They are already planning a similar experiment in primates, performing much more complicated tasks,