Next-generation neural interface: how a patient with ALS transmitted nearly 2 million words using the power of thought
The world of neurotechnology has achieved another breakthrough. Researchers from the University of California, Davis, have presented the results of long-term home use of a speech neurointerface by a patient with amyotrophic lateral sclerosis (ALS). Over 19 months, Casey Harrell transmitted 183,060 sentences — that's 1,960,163 words — at an average speed of 56 words per minute.
What is particularly important is that this is not a laboratory demonstration but real, everyday practice. The system operated without the presence of researchers, in a home environment, which fundamentally changes the perception of the practical applicability of such technologies.
Home Use: From Laboratory to Real Life
Harrell used the neurointerface for more than 3,800 hours. The system allowed him to communicate with family, friends, colleagues, and doctors, send messages and emails, participate in video calls, use the internet, and maintain full employment despite paralysis.
According to the patient's own assessment, the system decoded 92% of sentences as at least "mostly correct." In formal tests where Harrell was shown words on a screen, accuracy exceeded 99% with a vocabulary of 125,000 English words. The peak rate was 99.2%.
At the time of the study's publication, Harrell had used the system on 444 out of 653 days post-implantation. After his assistants were allowed to independently connect and disconnect the equipment without researchers present, the average daily interaction time increased from 3.7 to 9.5 hours.
How the System Works
In 2023, Harrell had four microelectrode arrays implanted in the left precentral gyrus — the brain region responsible for speech coordination. The system reads signals from 256 cortical electrodes when the patient attempts to speak.
An algorithm converts neural activity into phoneme probabilities every 80 milliseconds, and then a language model selects the most likely sequence of words from a vocabulary of approximately 125,000 words. The text is displayed on a screen in real time. After completing a phrase, the system can vocalize it using a synthesized voice tuned to sound like Harrell's voice before his illness.
To control the computer, the patient also used a cursor decoder. It was previously believed that speech and movement might require different brain areas, but the team showed that both modes can be implemented through signals from the speech motor cortex.
From Demonstration to Everyday Tool
The team had previously demonstrated the high accuracy of the neurointerface in laboratory sessions. In 2024, researchers reported that in the first 30-minute training session, the system achieved 99.6% accuracy with a 50-word vocabulary. On the second day, after an additional 1.4 hours of calibration, accuracy was 90.2% with a 125,000-word vocabulary.
The new work shifts the focus from controlled trials to long-term home use. This is one of the key steps toward practical neurointerfaces for people with severe motor impairments. Study co-author Sergey Stavisky stated that 3,800 hours of brain activity recording during system use represents, in his data, the largest individual dataset with single-neuron resolution.
However, the authors emphasize that the study describes a single clinical case. It is not yet known how well the results can be transferred to other patients, implantation sites, electrode types, or neurological conditions. The system also remains experimental: it uses wired connections, requires daily setup by trained assistants, and due to the size of the equipment, is only suitable for home use.
Against this backdrop, in March, Neuralink CEO Elon Musk reported that their BCI device could restore speech to those who have lost it. One patient, by day 80 of using the neuroimplant, was able to launch World of Warcraft and play using the power of thought. In April, it became known about brain-computer interface user Galen Buckwalter, who learned to create music with his thoughts. And in the spring, a startup founded by a former Neuralink president announced plans to test a biohybrid chip in humans.
Expert opinion: This case demonstrates that neurointerfaces are moving from futuristic experiments to real tools for improving quality of life. However, widespread adoption will require solving problems of miniaturization, wireless data transmission, and adaptation to various neurological conditions. For now, this is an impressive but singular success that sets the direction for the entire industry.