The participant in the 2023 Metzger study was implanted with a 253-channel high-density electrocorticography (ECoG) array, placed on the surface of the brain.

Checked against its source on October 17, 2026

In the source's own words

“A brainstem-stroke survivor with anarthria was implanted with a 253-channel high-density ECoG array 18 years after injury.”

A high-performance neuroprosthesis for speech decoding and avatar control, Sean L. Metzger et al., Nature (open full text via PubMed Central), 2023, Results, participant description.

What it measures: ECoG records electrical activity from electrodes placed on the surface of the brain under the skull, during surgery. The array was placed over the speech areas of the sensorimotor cortex.
What it does not show: One participant, implanted through surgery. This is the recording method behind the 78 words per minute result, not a method that a consumer device could use.