Brain implant helps stroke victim speak again

时间:2019-03-01 02:05:00166网络整理admin

By Colin Barras Video: An implant and specialised software have been used to interpret a paralysed man’s brain signals and produce recognisable sounds Nine years ago, a brain-stem stroke left Erik Ramsey almost totally paralysed, but with his mental faculties otherwise intact. Today he is learning to talk again – although so far he can only manage basic vowel sounds. In 2004, Ramsey had an electrode implanted in his speech-motor cortex by Philip Kennedy’s team at Neural Signals, a company based in Duluth, Georgia, US, who hoped the signal from Ramsey’s cortex could be used to restore his speech. Interpreting these signals proved tricky, however. Fortunately, another team headed by Frank Guenther at Boston University, Massachusetts, US, has been working on the same problem from the opposite direction. Guenther and his colleagues have used information from brain scans of healthy patients to monitor neural activity during speech. These studies show that the brain signals don’t code for words, but instead control the position of the lips, tongue, jaw and larynx to produce basic sounds. Guenther’s research group then developed software that could recognise and translate the patterns of brain activity during speech. When they teamed up with Kennedy, they could use their software to interpret the signals from Ramsey’s implanted electrode and work out the shape of the vocal tract that Ramsey is attempting to form. This information can then be fed to a vocal synthesiser that produces the corresponding sound. The software is now translating Ramsey’s thoughts into sounds in real time, so Ramsey hears his “voice” as he makes a sound, effectively bypassing the damaged region of his brain stem. This gives Ramsey immediate feedback on his pronunciation, which he can use to rapidly hone his speaking skills in the same way infants do when learning to talk. Initially, when prompted to produce a vowel sound such as “ee” or “oh”, he hit the correct sound around 45% of the time. Over the course of a few weeks, Ramsey’s accuracy has risen to 80%. In the future, Guenther says that the goal is to give Ramsey the ability to speak complete words with fluency, but that will require software and hardware improvements. “The synthesiser is good for vowels, but not for consonants,” he says. “We’re going to move to a synthesiser with better consonant capabilities, where the patient would have more control over jaw height, for instance.” But a more complicated system would be harder to control, says Guenther. “Right now, Erik is controlling two dimensions to create vowels,” he says. “But for consonants he would need seven dimensions – three to control tongue movement, two for lip movement, and one each for jaw and larynx height.” Klaus-Robert Müller at the Technical University of Berlin in Germany is intrigued by the study, but wonders whether it will come at a price for Ramsey. “If you’re trying to help someone to communicate with the external world, the question is how strenuous and stressful is the interface,” he says. “Some brain control interfaces can lead to migraines.” Ramsey still retains control of one muscle in his eye, through which he can communicate. Although that communication route is very slow, Müller thinks it might produce more data given sufficient time. He also thinks that Guenther and Kennedy’s technique might not be suitable for fully “locked-in” patients, who can’t control any muscles. “If you have a completely locked-in patient then maybe the brain begins to degrade because they’re not able to control anything,