How the brain produces speech – National Institutes of Health (NIH) (.gov)

Speech and language rely upon our means to supply all kinds of sounds in a selected order. How the neurons within the human mind work collectively to plan and produce speech stays poorly understood.

To start to deal with this query, an NIH-funded group of researchers, led by Drs. Ziv Williams and Sydney Money at Massachusetts Normal Hospital, recorded neuron exercise throughout pure speech in 5 native English audio system. The experiments have been completed whereas individuals have been having electrodes implanted for deep mind stimulation. The researchers recorded neurons in a prefrontal mind area recognized to be concerned in phrase planning and sentence development. They used high-density arrays of tiny electrodes that would document indicators from many particular person neurons directly. Their outcomes appeared in Nature on January 31, 2024.

The scientists discovered that the exercise of virtually half the neurons trusted the actual sounds, or phonemes, within the phrase about to be mentioned. Some neurons, as an illustration, grew to become extra lively forward of talking the sounds for “p” or “b”, which contain stopping airflow on the lips. Others did so forward of talking “ok” or “g” sounds, that are fashioned by the tongue in opposition to the taste bud. Furthermore, sure neurons appeared to mirror the precise mixture of phonemes within the upcoming phrase. The group discovered that they might predict the phonemes that made up the phrase about to be spoken primarily based on the exercise of those neurons.

For a couple of quarter of the neurons, exercise additional mirrored particular syllables, or ordered sequences of phonemes which may be all or a part of a phrase. The group might predict the syllables within the upcoming phrase utilizing the exercise from these neurons. These neurons didn’t reply to the phonemes within the syllable by themselves. Nor did they reply to the phonemes out of order or break up throughout completely different syllables.

A minority of neurons responded to the presence of prefixes or suffixes. These are examples of morphemes, or teams of sounds that carry particular meanings. The presence of morphemes within the upcoming phrase may very well be predicted from these neurons’ actions.

The group additionally discovered that completely different units of neurons activated in a selected order. The morpheme neurons activated first, round 400 milliseconds (ms) earlier than the utterance. Phoneme neurons activated subsequent, round 200 ms earlier than the utterance. Syllable neurons activated final, round 70 ms earlier than utterance. Most neurons responded to the identical characteristic (phoneme, syllable, or morpheme) each earlier than and through the utterance. However the exercise patterns through the utterance differed from these earlier than it. Lastly, the group discovered that neurons that responded to speech sounds throughout talking differed from those who responded to those self same speech sounds throughout listening.

In an accompanying paper in the identical situation of Nature, one other analysis group used the identical approach to look at how neurons in one other space of the mind reply whereas listening to speech. They equally discovered that single neurons encoded completely different speech sound cues.

The findings counsel how numerous components of speech are encoded within the mind, and the way the mind combines these components to type spoken phrases. This data may assist in creating brain-machine interfaces that may synthesize speech. Such gadgets might assist a spread of sufferers with circumstances that impair speech.

“Disruptions within the speech and language networks are noticed in all kinds of neurological problems—together with stroke, traumatic mind damage, tumors, neurodegenerative problems, neurodevelopmental problems, and extra,” says co-author Dr. Arjun Khanna. “Our hope is that a greater understanding of the fundamental neural circuitry that permits speech and language will pave the way in which for the event of remedies for these problems.”

—by Brian Doctrow, Ph.D.