A man with severe paralysis, unable to move most of his body, has found a way to communicate using an experimental brain implant. This technological breakthrough allows his family to hear his voice again as a digital version vocalizes his thoughts.
Casey Harrell, who is 47 years old, suffers from an advanced form of amyotrophic lateral sclerosis (ALS), making his natural speech difficult to comprehend. However, given the chance, Harrell has much to convey.
For nearly two years, Harrell has been connected to a continuously operating brain-to-text decoder through an experimental neuroprosthetic device. This advanced interface has enabled him to articulate over 183,000 sentences and nearly 2 million words.
The technology involves a surgical implant in a specific brain region. Electrode arrays in this area can detect neurological activity linked to speech attempts, even if the individual cannot move their mouth.
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This neurological data is automatically picked up by an external speech decoder, which displays the information on a computer screen in real time. Harrell uses his eye gaze to navigate the screen; his focus is shown as a white circular cursor, and he can ‘click’ using thought alone.
Setting up the device takes some time each morning, with assistance from a caregiver. Once ready, the decoder, mounted on a mobile cart, accompanies Harrell throughout his day. This setup allows him to independently send emails, browse the internet, and maintain full-time employment.
Most importantly, Harrell can communicate with his loved ones. His digital voice has been designed to resemble his voice before ALS.
“It is very sweet to have the ability to look at my wife’s eyes when she hears my voice,” Harrell expressed through the system. “It conjures up a sweet memory and allows me to explain to my daughter, who does not remember much about when I was still talking to them, and remind them of what I used to sound like.”
This development has been transformative, as Harrell himself has shared. In the video below, Harrell explains via text that the technology enables him “to do so very much and stay tethered to my life as a human being.”
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His experience gives scientists hope that these experimental devices might be viable in broader applications and over the long term. “For years, BCIs have been proof-of-concept devices that lived in highly controlled research labs,” notes neurosurgeon David Brandman, a co-principal investigator and co-senior author of the study from the University of California, Davis (UCD).
“This work shows that we may have crossed a threshold by empowering a person with paralysis to speak on his own terms.”
Harrell participates in an ongoing pilot clinical trial in the US called BrainGate 2, led by Brandman and his team. This preliminary study assesses the safety and feasibility of a novel brain-computer interface for individuals with paraplegia who have severe speech impairments or cannot use their hands.
The technology was developed at UCD, in collaboration with experts at Brown University and Mass General Brigham Neuroscience Institute.
Initially, Harrell could only use the system with researcher support. Now, thanks to several significant adjustments, he can operate it almost entirely independently from his home.
According to researchers at UCD, who have various levels of involvement in the technology, Harrell has amassed the trial’s largest brain recording dataset to date. Over 400 days, he has logged more than 3,800 hours using the device. Harrell’s average communication speed is approximately 56 words per minute, a notable improvement from when he first started converting his thoughts into text in 2023.
“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 at the UC Davis Neuroprosthetics Lab. “Sometimes, he would do that over 12 straight hours.”
Importantly, Harrell also has control over his silence, with a ‘privacy mode’ that allows him to keep certain thoughts to himself. Only data from sessions without this ‘privacy mode’ were saved and used to develop future speech-decoding models.
When Harrell uses the system, the program accurately captures his thoughts about 92 percent of the time, according to recently published results. This newfound independence has been transformative for Harrell, echoing the experiences of others with brain-computer interface technology.
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“It is a life that is more full of dynamic action and with friends and family, with colleagues,” Harrell shared through the device, “and it is something that allows me to communicate more in my natural way of communicating than any other technology that I have experienced.”
Researchers aim to use Harrell’s experience and insights from the 26 other participants in the clinical trial to refine the technology for future users.
The study’s findings are available in Nature Medicine.
