Brain implants could help translate paralyzed patients’ thoughts into speech
A group of US scientists is working on a brain implant, which they hope could improve communication for people who can’t talk.
The implant, developed at the Feinstein Institute for Medical Research in New York, would sit on the surface of the brain and detect the electrical impulses it generates. Tiny electrodes would be used to pick up activity in areas that listen to and formulate speech; these would then be transmitted wirelessly to a computer. In turn, the computer would decode the transmissions and use a vocoder to synthesise them back into sounds.
Brian Pasley, a research scientist at the University of California, Berkeley, whose research has included similar work, said: “We think we’re getting enough of an understanding of the brain signals that encode silent speech that we could soon make something practical. Even something modest could be meaningful to patients. I’m convinced it’s possible.”
Cranial complexities
When the brain imagines something, the activity is very similar to when you actually do it – so thinking about saying something or movingcreates the same patterns of brain activity as carrying out those actions.
The implant system, however, is a long way from being workable – and workable would mean communicating simple ideas, such as yes or no, I’m hungry or I’m thirsty, rather than long speeches.
Brain implants are tricky to say the least: they have a history of problems, which means that more than a decade after the first prototypes the technological advances are limited. Some of the implants have damaged the brain or been rejected by the nervous system; others need to be hooked up to cables and electronic equipment. They also don’t last forever, so brain surgery would be needed multiple times during a person’s lifetime to replace them.
Scientists who have tried to develop brain implants in the past have mostly worked on movement and sensation – reading electrical signals in the motor cortex corresponding to the intention to move, and translating the signals into instructions to operate a computer cursor or robotic arm.
Speech has proved more problematic. Neuroscientist Frank Guenther, from Boston University, and neurologist Phil Kennedy actually developed the first speech implant in 2007, using electrodes implanted in the brain of a man with locked-in syndrome. The electrodes picked up signals corresponding to moving the tongue, lips, larynx, jaw and cheeks to produce particular sounds.Unfortunatelyhowever, Kennedy fell foul of the US health authorities and was barred from continuing his work.
The speech systems we have at the moment work by getting patients to look at a screen with letters on. Electrodes on their scalp detect the brain waves that correspond to eye movement – so as the person looks in turn at the letters that spell the word they want, the computer decodes their eye movements and produces the words through a speech synthesiser. The late cosmologist Stephen Hawking, who suffered from motor neurone disease, used a system like this.
So what’s the latest development?
Electrical engineer NimaMesgarani, from Columbia University, is leading the latest project in collaboration with Dr Ashesh Mehta, a neurosurgeon at the Feinstein Institute.Their implant has been tested on just five volunteers who were already having brain surgery for epilepsy. During the surgery, Mehta placed electrodes on the surface of their auditory cortex – the part of the brain that processes speech.
The volunteers listened to people speaking for half an hour, and the software recorded their brain activity and worked out which electrical signals corresponded to which sounds. The information was then sent to a vocoder which would produce the words.
Whereas previous efforts had often produced little more than a stream of unintelligible noise, this time the scientists reported that intelligibility reached 75 per cent. Their draft paper is publicly available on the bioRxivwebsite, but has not yet been peer reviewed.The next step is to test the software on brain signals evoked by imagining speaking.
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