Independent Speech Brain-Computer Interface Empowers ALS Patient Casey Harrell

In July 2023, UC Davis neurosurgeon David Brandman and his team implanted four intracortical microelectrode arrays (256 electrodes) into the left precentral gyrus of 45-year-old Casey Harrell, diagnosed with amyotrophic lateral sclerosis. The arrays feed neural activity from the speech-motor cortex to external hardware that converts it into phonemes, words and cursor commands. Six months after surgery Harrell began operating the system at home without researcher assistance, and over two years accumulated more than 3,800 hours.

MIT Technology Review

Brain-computer interfaces have traditionally required researcher setup and short-term testing. The BrainGate2 trial, conducted with Brown University and the Mass General Brigham Neuroscience Institute, targeted independent at-home operation and long-term reliability.

Brain-computer interface enables independent, accurate communication for man living with ALS

Harrell logged >3,800 hours, generated 183,000 sentences (~2 million words) and typed at 56 wpm. Controlled testing showed 99 % word accuracy with a 125,000-word vocabulary; early trials recorded 99.6 % accuracy on a 50-word set and 97.5 % on the expanded lexicon. He rated 92 % of sentences as accurate or mostly correct.

Brain-computer interface enables independent, accurate communication for man living with ALS

Independent, high-fidelity communication restores social interaction, enables work and eases caregiver load for people with severe motor loss. The trial also produced the largest single-subject, single-neuron brain-recording dataset, a valuable resource for basic speech research. The results suggest a shift toward broader clinical adoption of intracortical BCIs for ALS, spinal-cord injury and related conditions.

Brain-Computer Interface Empowers ALS Patient with Independent and Precise

Neurosurgeon David Brandman emphasizes that patient participation made the advance possible and foresees benefits for neurological disorders. Neuroengineer Nicholas Card highlights the system’s robustness, noting sessions exceeding twelve hours without researcher help. Neuroscientist Sergey Stavisky points to the unprecedented volume of single-neuron recordings, while the team describes the work as a threshold crossing from proof-of-concept to practical assistive technology.

Brain-Computer Interface Empowers ALS Patient with Independent and Precise

Speaking through the implant, Harrell describes his life as “more full of dynamic action” and says the system lets him “communicate in my natural way… more than any other technology.” He also notes the impact of hearing his voice recognized by his wife and daughter.

Brain-computer interface enables independent, accurate communication for man living with ALS

Sources list Harrell as 45 at implantation in July 2023 and as 47 in later descriptions, creating an age discrepancy. Several source reliability scores are low, and the findings rely on a single participant, limiting generalizability.

Brain-Computer Interface Empowers ALS Patient with Independent and Precise

“For years, BCIs have been proof-of-concept devices that lived in highly controlled research labs.” — David Brandman, UC Davis neurosurgeon, co-principal investigator

Brain-computer interface enables independent, accurate communication for man living with ALS

“This work shows that we may have crossed a threshold, by empowering a person with paralysis to speak on his own terms,” said UC Davis neurosurgeon David Brandman.” — David Brandman, UC Davis neurosurgeon, co-principal investigator

Brain-computer interface enables independent, accurate communication for man living with ALS

“As far as we know, these 3800 hours of brain recording as Casey used the system is by far the largest individual brain recording dataset with single neuron resolution.” — Sergey Stavisky, neuroscientist, co-director of the UC Davis Neuroprosthetics Lab

Brain-computer interface enables independent, accurate communication for man living with ALS