For Casey Harrell, the brain implant is part of daily life now. He uses it to talk with friends and family, read to his young daughter, surf the web, and do his job, nearly three years after electrodes were implanted in his brain.

Harrell has amyotrophic lateral sclerosis, or ALS, and is paralyzed. He first used the brain-computer interface, or BCI, to “speak” sentences with help from a research team in 2023. Since then, he has logged thousands of hours on the device and can use it largely independently after being “plugged in” by a carer.

Within the first 22.6 months after the implant, Harrell used it for more than 3,800 hours at home without researchers present, according to a report published today in Nature Medicine.

“He’s the first power user of a speech BCI,” said team member Sergey Stavisky, a neuroengineer at the University of California, Davis.

Three years ago, Harrell agreed to take part in the trial led by David Brandman, an associate professor of neurological surgery at the University of California, Davis, and his colleagues. Harrell was 45 at the time and had already been diagnosed with ALS, which had left him dependent on others to control his wheelchair and to dress and feed him. People also struggled to understand his speech.

“The industry was [on the] cusp of a transformation, and I wanted to be part of it,” Harrell said.

In July 2023, doctors implanted four arrays of 64 electrodes each into Harrell’s brain during a five-hour operation. Each pair of arrays was wired to a “pedestal” connection point, creating two docking locations on the outside of his skull that connect the electrodes to a computer.

The system records activity from the speech motor cortex, a region involved in the movements that allow people to speak. Nicholas Card, a neuroengineer at UC Davis and a member of the team, said the process works by decoding sounds first and words second.

“There are 39 phonemes that make up all the sounds in the [American] English language,” Card said.

“We first go from brain data to phonemes, and then from phonemes to words,” he said.

The team started using the device about a month after surgery. Card said Harrell’s speech decoder worked on the first day. In August 2023, Harrell used the device with a 50-word vocabulary, and 99.6 percent of the words matched what he intended. That vocabulary was later expanded to 125,000 words with 97.5 percent accuracy.

The team said the system is now 99 percent accurate.

Harrell can also control a cursor, which lets him use his personal computer to send text messages and emails, surf the web, and keep up with his work as an environmental activist.

In 2023, research team members had to visit Harrell’s home and physically connect and disconnect him from the device. The system has since been automated further, and now Harrell’s care partner can put it on and take it off for him.

“He’ll wake up, get plugged in, and just get going,” Stavisky said.

Mariska Vansteensel, a BCI researcher at Utrecht Medical Center who was not involved in the trial, said that matters for patients.

“For these technologies to be relevant for patients, we really need to test them in settings in which they will eventually be used … to demonstrate that it has value, that it’s usable, and that it functions well without the constant involvement of a research team,” she said.

The team has also added features Harrell asked for. He can switch on a “privacy mode,” which automatically deletes decoded text, and he can use a “profanity filter” while talking to his young daughter.

“We have been able to add on to the software side of the device … improving the accuracy and adding more bells and whistles to enable me to be more independent when using the device,” Harrell said. “We are making the road as we walk it, or roll it, so to speak.”

Vansteensel said the strong results in Harrell do not mean the device will work as well, or as long, for everyone with ALS. She said a woman with ALS she worked with used a fully implanted device for seven years before it stopped working near the end of that period, apparently because of brain degeneration.

Jane Huggins, who develops noninvasive BCIs at the University of Michigan and was not involved in the trial, said not everyone with ALS will want invasive brain surgery.

“Long-term, independent use with efficient and accurate communication is kind of the holy grail of BCI,” she said. “But we have been finding a consistent aversion to hospital stays among people with progressive conditions like ALS.”

Harrell said the device has changed what he can do for his family and for himself.

“Living with a disease like ALS, you are supposed to have diminished dreams. I do not,” Harrell said. “Any one of these things would be an absolute godsend of improvement. To have all of them, and many, many more, is truly revolutionary.”

“This has allowed me to keep working and earn money and insurance for my family. This is reconnecting me with friends and family who are too shy or too afraid to come over and not be able to understand me,” Harrell said.

“With my seven-year-old daughter, I am able to create a bond that I wasn’t before able to forge. Now I can read to them and help them sharpen their own reading skills. By doing so, I am able to share the responsibility of parenting with my wife, who does so much caregiving for me and also our daughter.”

Researchers are still trying to improve the system. One goal is a “brain-to-voice” setup that could decode brain activity directly into a speaking voice with cadence, inflection and intonation.

“We’re never satisfied,” Stavisky said.

Read more from MIT Technology Review.