Casey Harrell lost his voice to ALS or amyotrophic lateral sclerosis. As a volunteer in a clinical trial, he’s helping scientists test a brain-computer interface. Electrode arrays that are implanted in Casey’s brain send signals to nearby computers, where those signals are translated into words he intended to say.

Casey uses this system every day to talk with his wife, daughter, friends and work colleagues. The moment he realized that it worked was “pure joy,” Casey says. Even though the researchers scripted his words for that first test, “it was a profound moment,” he says. “The possibilities for the near future for me and the rest of humanity were overwhelming to realize.”

This episode of The Deep End: Talk to Me follows Casey and the fast-moving neuroscience that enables him to speak.

Episode 4 transcript Patients paralyzed from the neck down can manipulate robotic arms with their thoughts. The woman in this video is controlling a robot with her mind.…