A brain implant with AI decoding lets Casey Harrell, who lost his speech to ALS, talk with family and work from home, nearly 2 million words so far

Casey Harrell lost his speech to ALS. Since 2023, electrodes in his brain’s speech area, plus AI that turns their signals into words, have let him talk again. A peer-reviewed Nature Medicine study counted 1,960,163 words over nearly two years of home use at 56 words a minute, and he rated 92% of his sentences at least mostly correct.

Casey Harrell began losing his speech soon after an ALS diagnosis in 2020. By the time of his surgery, only his wife, Levana, and his assistant could fully understand him, and he didn’t join even a video call without one of them there to translate. In July 2023 he joined the BrainGate2 clinical trial at UC Davis, where a neurosurgeon placed four tiny electrode arrays on the part of his brain that controls speech.

The clever bit

When Harrell tries to say something, 256 electrodes pick up the signals his brain sends toward the muscles of his mouth and throat. Machine learning matches those patterns to 39 English speech sounds, and a language model assembles the sounds into words and sentences. The words appear on a screen, he proofreads them, and the computer can say them out loud.

On the second day of testing, with a 125,000-word vocabulary switched on, his second sentence was “I’m looking for a cheetah.” Leigh Hochberg, the BrainGate director watching on a video call, was sure the decoder had slipped. He couldn’t see that Harrell’s 4-year-old daughter had just bounded into the room in her cheetah costume.

A study in Nature Medicine in June tracked what came after. Over nearly two years, Harrell used the system at home for more than 3,800 hours with no researchers present. He communicated 183,060 sentences, close to 2 million words, at an average of 56 words a minute. He rated 92% of the sentences at least mostly correct, and in formal tests the decoder got more than 99% of words right.

It was so amazing to be able to be understood right from the get-go and to be able to talk and respond to my daughter, especially because that was lacking completely from my life.

— Casey Harrell, BrainGate2 trial participant at UC Davis, via sciencenews.org

Hooray

Harrell works full time again. He talks through the system for about 10 to 14 hours a day, sending email and Slack messages, playing Wordle with his wife and daughter, and getting a new climate consultancy project off the ground.

What comes next

For now the device is wired and stays at home. Other teams are testing fully implanted, portable versions, and UC Davis said in June that the BrainGate2 trial was still enrolling. Harrell’s hope is a day when he is one of many users instead of one of one.

How solid is it?

Testing: Early research, prototypes or preprints. Encouraging questions, not established benefits.

Investigational device in the BrainGate2 clinical trial at UC Davis Health. The peer-reviewed results in Nature Medicine (Card et al., June 15, 2026) cover more than 3,800 hours of home use with no researchers present over nearly two years: 183,060 sentences, 1,960,163 words, 56 words per minute on average, 92% of sentences rated at least mostly correct by Harrell, and more than 99% word accuracy in formal tests with a 125,000-word vocabulary. Science News (Laura Sanders, October 15, 2026) interviewed Harrell and the research team for its own feature.

See for yourself.

Selected for Nov 2, 2026. Reviewed Nov 2, 2026, 9:39 AM MT. Source dates may be earlier than this edition.