In a first, brain implant lets man with complete paralysis spell out thoughts: ‘I love my cool son.’

In its final stages, the neurological disease amyotrophic lateral sclerosis (ALS) can bring extreme isolation. People lose control of their muscles, and communication may become impossible. But with the help of an implanted device that reads his brain signals, a man in this “complete” locked-in state could select letters and form sentences, researchers report this week.

“People have really doubted whether this was even feasible,” says Mariska Vansteensel, a brain-computer interface researcher at the University Medical Center Utrecht who was not involved in the study, published in Nature Communications. If the new spelling system proves reliable for all people who are completely locked in—and if it can be made more efficient and affordable—it might allow thousands of people to reconnect to their families and care teams, says Reinhold Scherer, a neural engineer at the University of Essex.

ALS destroys the nerves that control movement, and most patients die within 5 years of diagnosis. When a person with ALS can no longer speak, they can use an eye-tracking camera to select letters on a screen. Later in the disease’s...