Brain-computer interface technologies are advancing from experimental stages to clinical trials, offering new communication avenues for individuals with paralysis, though challenges remain in regulatory approval and participant safety.
As technological advancements bridge the gap between science fiction and reality, brain-computer interfaces (BCIs) are beginning to undergo clinical trials aimed at assisting individuals with paralysis. These systems have shown promise in translating neural signals into actions such as cursor movement, robotic-arm control, and even synthesized speech. The case of Casey Harrell, a 47-year-old man suffering from amyotrophic lateral sclerosis (ALS), exemplifies the potential and limitations of these emerging technologies.
In 2023, Harrell underwent a procedure led by UC Davis neurosurgeon David Brandman, who implanted four microelectrode arrays in the left precentral gyrus of his brain, the area responsible for muscle coordination necessary for speech. Over the span of nearly two years, Harrell utilized this system in his home, independently generating over 183,000 sentences at an average rate of 56 words per minute, as reported by Brandman, neuroscientist Sergey Stavisky, and their colleagues in a June 2026 publication in Nature Medicine. While this speed falls short of normal conversational rates, it does enable functional communication, a significant breakthrough for individuals with severe speech impairments.
It is important to clarify that these systems do not ‘read thoughts’ in the traditional sense. Instead, the electrodes detect signals from the brain related to the commands sent to the muscles involved in speech. A trained model interprets these signals, converting them into phonemes, which are then synthesized into speech that resembles Harrell’s voice prior to his illness.
Progress and Accuracy
The accuracy of these systems has significantly improved over time. An earlier version of a similar BCI, detailed in a 2024 New England Journal of Medicine study by Nicholas Card and colleagues, achieved 97.5% accuracy over approximately eight months, with a vocabulary of 125,000 words and a rate of 32 words per minute. The 2026 follow-up not only increased accuracy to above 99% in controlled tests but also nearly doubled the speed of output, marking a shift from laboratory settings to real-world application.
Limited Participant Numbers
Despite the promising results, the actual number of individuals who have received these implants remains notably low. A comprehensive review by K. Michelle Patrick-Krueger and colleagues, published in Nature Reviews Bioengineering, documented 67 participants across 21 research groups from the first chronic implantation in 1998 through December 2023. This data reflects a slow progression over 25 years, with no BCI device approved for commercial sale as of yet.
Among the companies pioneering this technology, Neuralink has made the most rapid advancements in participant enrollment. As of January 2026, the company had enrolled 21 participants in various trials, with reports indicating no serious device-related adverse events. Participants have been able to control cursors, play video games, and, more recently, navigate powered wheelchairs. However, all of these applications remain investigational.
Different Approaches to BCI Implantation
There is an ongoing debate within the field regarding the optimal approach for BCI implantation. Neuralink employs a surgical robot to insert flexible electrodes directly into the motor cortex, which allows for high-quality signal acquisition but necessitates open-brain surgery. In contrast, Synchron has developed a less invasive method using its Stentrode device, which is inserted through the jugular vein and positioned against the motor cortex, reading neural signals through the vessel wall. This method offers a lower risk of surgical complications, but questions remain about whether the lower resolution of Stentrode can match the capabilities of Neuralink’s approach.
Challenges Faced by Participants
The experiences of participants in these trials highlight significant ethical and practical concerns. Ian Burkhart, paralyzed from the elbows down due to a diving accident, became the first person to regain hand movement through a BCI implanted in 2014. However, after seven years, funding for his trial ceased, and he experienced complications, including a persistent infection around the device. Burkhart articulated the emotional toll of regaining a function only to lose it again, stating that it felt like losing a part of his identity.
Moreover, there have been reports of other participants facing adverse outcomes, including one woman who had her implant removed against her will when the sponsoring company could no longer support the trial financially. These incidents have led ethicists, such as Marcello Ienca from the Technical University of Munich, to argue that such actions could violate human rights, raising critical questions about participant consent and the responsibility of companies to ensure ongoing support for their devices.
Future Directions and Regulatory Hurdles
Looking ahead, regulatory approval remains a significant barrier for further development and commercialization of BCI technologies. Currently, no permanently implanted motor or speech interface has received regulatory clearance. Synchron is working towards a pivotal trial that could support the first premarket approval filing for its device, bolstered by a $200 million Series D funding round in November 2025. Meanwhile, Neuralink’s pivotal trial design is still under consideration, and even under optimistic assessments, the timeline for prescription availability for these devices is measured in years rather than months.
As demonstrations of BCI capabilities continue to emerge, the focus shifts from technical challenges to the broader implications of these technologies. The story of Casey Harrell, who used his system to reconnect with his daughter’s memories of his voice, underscores the profound human element at the heart of these advancements. As the field progresses, it must confront the critical question of sustainability and ongoing support for the voices that these technologies aim to restore.
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