"Mr. Harrell’s team sank into his brain’s outer layer four electrode arrays that looked like tiny beds of nails."

"That was double the number that had recently been implanted in the speech areas of someone with A.L.S., or amyotrophic lateral sclerosis, in a separate study. Each array’s 64 spikes picked up electric impulses from neurons that fired when Mr. Harrell tried to move his mouth, lips, jaw and tongue to speak.Three weeks after surgery, scientists gathered in Mr. Harrell’s living room in Oakland, Calif., to 'plug him in,' connecting the implant to a bank of computers with cables attached to two metal posts protruding from Mr. Harrell’s skull."

From "A.L.S. Stole His Voice. A.I. Retrieved It. In an experiment that surpassed expectations, implants in a patient’s brain were able to recognize words he tried to speak, and A.I. helped produce sounds that came close to matching his true voice" (NYT)(free access link).

"After only briefly training the computers to recognize Mr. Harrell’s speech, the implant began recording what he intended to say from a 50-word vocabulary with 99.6 percent accuracy. The device worked so well, so soon, that the scientists had to cut an initial session from their analysis: Halfway through trying to speak his first prompt aloud — 'What good is that?' — a shaking, smiling Mr. Harrell crumpled into tears. To the average listener, 'what' and 'good' had come out of Mr. Harrell’s mouth muddled and indecipherable. But to the electrodes tuned to individual neurons in Mr. Harrell’s brain, the words were perfectly clear. A screen in front of him displayed exactly what he had been trying to say."