When Sergey Stavisky first started thinking about brain-computer interfaces (BCI) as an undergraduate at Brown University, he was motivated by three factors. “I liked building things,” he recalled, “and I wanted to do something medical. But I was also fascinated by the mind.”
That combination would lead Stavisky into a field that is now rapidly redefining what it means to lose, and potentially regain, a voice.
Today, Stavisky is an associate professor of neurological surgery at the University of California, Davis, and a leading figure in the development of AI-powered speech neuroprostheses. His work, recognized this year by the Chen Institute and Science Prize for Al Accelerated Research , sits at the intersection of neuroscience, clinical care and machine learning. But at its core is a simple goal: restoring the ability to speak to people who have lost it.
That goal becomes vivid in the story of one participant in his team’s research, a man living with amyotrophic lateral sclerosis (ALS) who could no longer speak intelligibly.
Through an implantable device and a suite of AI models trained on his brain activity that Stavisky and his team designed, the man is now able to generate fluent sentences – first as text, then as synthetic speech modeled on his own pre-ALS voice. In moments of daily use, he has produced millions of words.
Dealing with data overload
The science behind that achievement depends on a reality that has transformed neuroscience over the past decade: data overload. “Brain signals are really complicated,” Stavisky explained. Where researchers once recorded from single neurons, modern systems can capture signals from hundreds of neurons at a time. But the behaviors they are trying to decode, like speech, are among the most complex human actions, and traditional statistical methods for processing data, Stavisky said, simply break under such complexity.
He and his colleagues needed a way to process massive amounts of neural data very quickly and flexibly. “AI turned out to be uniquely powerful for that,” he said.
In Stavisky’s system, one model decodes brain activity into phonemes, the basic sound units of language. Another model, drawing on large language modeling approaches, converts those phonemes into words and sentences. In an alternative straight-to-voice approach, deep learning systems reconstruct speech sounds, producing a synthetic voice in real time.
The result is a system that can translate intention into speech with fidelity, generating audible sounds with delays as short as 30 milliseconds. This is fast enough to approximate natural conversation.
In a study published in Nature Medicine in June, Stavisky and colleagues describe how their BCI helped the participant with ALS to maintain rich interpersonal communication with his family and friends at home, independently control his personal computer, and sustain full-time employment.
“Stavisky developed an AI-based speech neuroprosthesis with immediate and transformative practical impact,” said Yury V. Suleymanov, senior editor at Science . “It restored communication for a paralyzed patient with amyotrophic lateral sclerosis with over 99% word accuracy, enabling the patient to express 2.7 million words over two years using only brain signals. His team achieved real-time voice synthesis, allowing the patient to modulate intonation and even sing.”
From movement to speech
Stavisky said a moment early in his career, while working on BCIs for movement, led him to pivot to focus on BCIs for speech. He had noticed something consistent across patients: restoring the ability to move a cursor or robotic arm was valuable, but restoring communication was always more urgent. “Communication was always the number one priority,” he said.
That realization, combined with emerging advances in machine learning and intracortical recording technology, led him to change mid-career from motor prosthetics to speech. At that time, speech decoding from brain signals was widely considered one of the hardest problems in neuroprosthetics. But progress in AI was accelerating at exactly the right moment. Even consumer dictation systems were beginning to reach usable performance levels around 2018, he said.
Looking ahead, Stavisky said the long-term goal is a “high-fidelity surrogate voice”—a system so natural that if someone were speaking on the phone, “you couldn’t tell it wasn’t their natural voice.” The future will likely involve devices that are smaller, fully implanted, and less visible than today’s research systems. It will also require moving from laboratory prototypes to widely available clinical tools.
Already, the field is expanding. Companies are beginning to enter clinical trials for speech BCIs, and academic labs are exploring whether similar approaches could help people with stroke-induced aphasia, cerebral palsy or other language disorders. The implications, Stavisky suggested, could extend far beyond paralysis.
"Ten years ago, Tianqiao and I founded the Chen Institute to pursue a fundamental question: how does the brain give rise to intelligence?,” said Chrissy Luo, Chen Institute cofounder. “We could not have imagined then that AI would change not just how we study the brain, but what we could learn from it. Dr. Stavisky's research has done something once considered nearly impossible: decode brain signals directly into speech, giving patients back the ability to communicate in their own voice. This prize was created for exactly this kind of work, and we are proud to celebrate his achievement alongside our partners at AAAS and Science . We remain committed to championing the researchers who are redefining what science can achieve."
Finalists
Finalists for the prize include Zhiling Zheng, for his essay , “Reprogramming Synthesis: General-Purpose AI Agents in the Materials Chemistry Laboratory.” The second finalist for the prize is Nicholas C. Jacobson, for his essay , “Generative AI to Scale Precision Evidence-Based Psychotherapy.”