The Transmitter reports:

Individual neurons in the cerebral cortex are finely tuned to the sounds of human speech—beyond just picking out consonants and vowels, two new independent studies show. The cells encode small sounds called phonemes that are said in a similar way; the order in which syllables are spoken; the beginning of sentences; vocal pitch; and word stress, among other features of speech.

The studies were able to reveal this new level of detail by using Neuropixels probes, which capture the activity of hundreds of individual neurons across all layers of the cortex. Past recordings made from the surface of the brain have found groups of neurons that tune to sequences of sound or certain articulation movements, such as the height of the tongue when people say vowels or the nasal sounds in the consonants “m” and “n.”

Now the Neuropixels data extend that 2D view into 3D and offer a “more fine-grain view of what is happening across different cortical layers,” says Kara Federmeier, professor of psychology and neuroscience at the University of Illinois, who was not involved in either study but studies speech by using electroencephalogram recordings from outside the skull. “It’s difficult to get that kind of information at any scale in humans.” [Continue reading…]