For decades, neuroengineers have dreamed of helping people who have been cut off from the world of language.

A disease like amyotrophic lateral sclerosis, or A.L.S., weakens the muscles in the airway. A stroke can kill neurons that normally relay commands for speaking. Perhaps, by implanting electrodes, scientists could instead record the brain’s electric activity and translate that into spoken words.

Now a team of researchers has made an important advance toward that goal. Previously they succeeded in decoding the signals produced when people tried to speak. In the new study, published on Thursday in the journal Cell, their computer often made correct guesses when the subjects simply imagined saying words.

Christian Herff, a neuroscientist at Maastricht University in the Netherlands who was not involved in the research, said the result went beyond the merely technological and shed light on the mystery of language. “It’s a fantastic advance,” Dr. Herff said.

The new study is the latest result in a long-running clinical trial, called BrainGate2, that has already seen some remarkable successes. One participant, Casey Harrell, now uses his brain-machine interface to hold conversations with his family and friends.

In 2023, after A.L.S. had made his voice unintelligible, Mr. Harrell agreed to have electrodes implanted in his brain. Surgeons placed four arrays of tiny needles on the left side, in a patch of tissue called the motor cortex. The region becomes active when the brain creates commands for muscles to produce speech.