How brain implants turn thoughts into speech.
Science News followed Casey Harrell, who has ALS, and the BrainGate 2 trial team as an implant in his speech motor cortex turns attempted speech into words at about 50 words per minute.
Casey Harrell began losing his ability to speak after an ALS diagnosis in 2020. In July 2023 he volunteered for the BrainGate 2 clinical trial, and UC Davis neurosurgeon David Brandman placed four small electrode arrays on the left side of his brain. Each array is about as wide as a peppercorn, and together they hold 256 electrodes.
The electrodes record electrical activity from the speech motor cortex as Harrell tries to speak. Wires carry the signals to nearby computers, where machine learning matches the patterns to 39 English phonemes, the basic sounds of speech. Language models then assemble the phonemes into words and sentences. Harrell reviews the text on a screen and approves it, and the system then says it aloud in a version of his own voice.
Brandman said Harrell can produce about six understandable words per minute when he tries to speak naturally. With the implant he reaches about 50 words per minute. Brandman put typical speech at 120 to 150 words per minute, which means Harrell is at roughly a third of that pace. Harrell said he uses the decoder 10 to 14 hours a day, seven days a week, and has done so for almost two years. He uses it to talk with his wife and daughter, friends and colleagues, and to write emails and messages.
In the first session, researchers gave Harrell a 50-word vocabulary. On the second, in early August 2024, they opened the system to a full English dictionary of more than 125,000 words. Leigh Hochberg, director of the BrainGate Consortium, said the system output "I'm looking for a cheetah," which he assumed was a decoding error. Harrell's four-year-old daughter had just walked in wearing a cheetah costume. Harrell called the early moments "pure joy."
Hochberg cautioned that the field is young. "We are at early days, just to be super clear." He said only a small handful of people worldwide have had an implanted brain-computer interface that decodes speech. The BrainGate trials have run for nearly 22 years, since the first implant in 2004.
The episode also covers the social side of slow communication. Harrell and others said conversation partners often grow impatient or assume that people who speak slowly do not understand. Brandman said clinicians sometimes confuse inability to communicate with lack of understanding.
Note: The headline says the implants turn thoughts into speech. The page describes a system that decodes brain signals from attempted speech in the speech motor cortex, not general thoughts.
At a Glance
- Casey Harrell, diagnosed with ALS in 2020, joined the BrainGate 2 trial in July 2023.
- His four implanted arrays carry 256 electrodes in total, and the system decodes brain signals into 39 English phonemes.
- He speaks about 50 words per minute with the implant, compared with about six without it, according to Brandman.
- On the second session in August 2024, researchers expanded his vocabulary from 50 words to more than 125,000.
- BrainGate trials have run for nearly 22 years, since the first implant in 2004.
Sources
This brief was written by Brightside Report from the reporting linked above. Spot an error? Request a correction.