A neuroprosthesis enables a paralyzed person to express himself

A paralyzed man who cannot speak or type words managed to express more than a thousand words thanks to a neuroprosthesis that translates his brain waves into real sentences, American scientists announced on Tuesday.

His favorite phrase was “Anything is possible,” said Sean Metzger of the University of California, San Francisco (UCSF), first author of the Nature Communication study.

A UCSF team showed last year that a brain-computer interface can express in spoken language 50 common words that people try to say.

A new study shows that the interface can decode all 26 letters of the international radio alphabet that people use to say words silently.

“When he said ‘cat’ (cat in English), he would say Charlie-Alpha-Tango,” Metzger told AFP.

The interface then uses a real-time language modeling system to determine the words or errors detected in the string of spoken letters.

The researchers thus managed to decode more than 1,150 words, which represents “more than 85% of the content of common English sentences”.

The simulation showed that this vocabulary could grow to more than 9,000 words, “the number of words most people use in a year,” Metzger said.

The interface could decode about 29 letters per minute, with an error rate of 6%. That’s about seven words per minute.

Metzger thinks the speed could be faster in the future, combining the interface’s ability to understand 50 common words with its understanding of the radio alphabet for less common words. The participant of the experiment was named BRAVO1, after the name of the interface (Brain-Computer Interface Restoration of Arm and Voice trial).

At the age of about 30, he suffered a stroke at 20, which caused him to suffer from anarthria, a language disorder that makes his words unintelligible, although his cognitive functions are intact.

He usually communicates using a lighted pen attached to his baseball cap, which allows him to point his head at the letters on the screen.

In 2019, researchers implanted a high-intensity electrode in his brain, above the motor cortex responsible for speech. They detect from the electrical impulses that are generated there when the patient tries to speak.

BRAVO1 “really enjoyed the experience because he can communicate with us quickly and easily,” Mr. Metzger said.

“I learned a lot about him,” he added, asking the patient to say what he wanted. For example, that he “absolutely did not like the food he lived in”.

A Stanford University study last year showed that a brain-computer interface can decode 18 words per minute when a participant imagines writing sentences. But according to Mr. Metzger, the “best of both worlds” is an interface that combines word detection and the phonetic alphabet.

The experiment, which needs to be validated with other participants, is still far from being available to the thousands of patients who lose their speech each year due to stroke, accidents or disease.

Professor of neuroprosthetics at UK’s Newcastle University, Patrick Degenaar, hailed the “very impressive results”. Because this type of surgery is “very invasive and high-risk,” he estimated that such a device will only be able to be used on a very small number of patients in the near future.

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