Brain-Computer Interface Restores Voice for ALS Patient

Casey Harrell, a 47-year-old with advanced ALS, received a surgical implant of electrode arrays in the speech-motor cortex in early 2023. The arrays feed a brain-computer interface that converts neural firing into text, which a speech synthesizer renders in a voice modeled on Harrell’s pre-ALS tone. After two years, Harrell operates the system independently from a mobile cart, enabling real-time conversation without researcher assistance.

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Brain-computer interfaces have previously been limited to tightly controlled labs. The BrainGate 2 pilot trial, launched by UC Davis with Brown University and Mass General Brigham, tests safety and feasibility for people with severe speech loss, marking the first unsupervised home use.

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Harrell has logged over 3,800 hours of neural recording across 400 days, the largest single-subject dataset with single-neuron resolution. The decoder averages 56 words per minute, has generated more than 183,000 sentences (?2 million words), and shows accuracy reported between 92 percent and over 99 percent. A user-activated privacy mode can halt data capture.

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The interface lets Harrell send emails, browse the internet and keep a full-time job without assistance. A synthetic voice, tuned to his pre-ALS timbre, lets his wife hear a familiar sound and his daughter recall his former speech. Harrell calls the experience a “life full of dynamic action” that restores his natural communication style.

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UC Davis investigators stress that BrainGate 2 assesses safety and functional feasibility for severe paralysis. They say Harrell’s extensive recordings will sharpen decoding algorithms and deepen insight into neural speech, viewing the trial as a threshold that could speed future therapies.

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Sources differ on accuracy, citing 92 percent versus over 99 percent correct transcription. Long-term implant durability and broader applicability across diverse ALS populations remain unaddressed.

Brain-Computer Interface Enables ALS Patient to Accurately Communicate

• “It is very sweet to have the ability to look at my wife’s eyes when she hears my voice and conjures up a sweet memory,” — Casey Harrell

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• “For years, BCIs have been proof-of-concept devices that lived in highly controlled research labs,” — Dr. David Brandman

Brain-Computer Interface Enables ALS Patient to Accurately Communicate

• “This work shows that we may have crossed a threshold by empowering a person with paralysis to speak on his own terms.” — Dr. David Brandman

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• “Casey can use the system to communicate his own thoughts, not only while we're there in a controlled environment, but whenever he wants," says Nicholas Card, postdoctoral scholar, UC Davis Neuroprosthetics Lab "Sometimes, he would do that over 12 straight hours.” — Nicholas Card

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The BrainGate 2 trial will enroll 26 additional participants, using Harrell’s dataset to improve decoding fidelity and expand vocabulary coverage. Results published in *Nature Medicine* signal a path toward broader clinical deployment.

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