How the Brain Decodes Speech: Special Neurons Process Specific Sounds

Delicate probes, as thin as wires, inserted into the brains of living individuals reveal the functions performed by individual neurons.

An unparalleled degree of insight into how humans comprehend speech has been made possible by recordings from hundreds of individual neurons while patients undergoing brain surgery listened to this and 199 other sentences. The findings indicate, for instance, that some speech-processing neurons become more active in response to particular speech sounds, such at the beginning of a sentence or the nasal sounds “m” and “n.” Today, Nature reports on the work.

Unlocking Language Neurophysiology

The research opens up new avenues for studying language neurophysiology, or how the brain interprets speech. Tim Harris, a measurement scientist at the Howard Hughes Medical Institute Janelia Research Campus in Ashburn, Virginia, compares it to traveling to the moon. Harris developed the technology that allowed the task to be done, but he was not directly involved in it.

According to William Muñoz, a neuroscientist at Massachusetts General Hospital in Boston who was not involved in the study, language neurophysiologists have been waiting for this crucial evidence for a very long time.

Almost 1,000 sensors in one probe

In order to comprehend brain activity, neurophysiologists have frequently depended on aggregate measurements from dozens to thousands of neurons. However, neuroscientist Angelique Paulk of Massachusetts General Hospital, who was not involved in the study, compares attempting to learn about a single neuron with such observations to standing outside a Taylor Swift concert and trying to pick out what specific fans are yelling by listening to the scream of the entire audience.

Luckily, co-lead authors of the work, neuroscientists Matthew Leonard of the University of California, San Francisco, and Laura Gwilliams of Stanford University in California, say that more resolution is now possible because of a recently created technology called Neuropixels.

A neuropixel probe is a centimeter-long, wire-thin rod covered in almost a thousand sensors, each of which can identify electrical impulses from a single neuron. Many of the sensors throughout the probe’s length connect with various neurons after it has been inserted into the brain tissue. The probe reads the activity in the neurons that the sensors are contacting.

Researchers can record data from one to several hundred neurons each time the device is implanted.

Mapping Specific Functions in the Superior Temporal Gyrus during Speech Perception

Leonard, Gwilliams, and associates recorded data from eight people who were listening to 200 English sentences from the superior temporal gyrus, an auditory area of the brain. Certain areas throughout the probe’s length appeared to have specific purposes, such as responding to vowels or the rising intonation that denotes a query. However, each region also had neurons that served purposes unrelated to its specificity.

The brain can process temporary information with the help of a combination of neurons with varying activities. For example, according to Leonard, this process occurs very rapidly and the information disappears once it is processed. The brain’s ability to integrate information and respond quickly may be aided by neural synapses that complement each other.

Study Unveils Creation Process of Vowel Representation in the Brain

The results contribute to understanding the brain’s functioning by revealing the process of vowel representation creation, according to Gwilliams. It goes beyond simply stating where vowels are located to explaining the formation of their representation.

The work is the first to offer such comprehensive information. It is just the third article to define the use of Neuropixels in humans.

Converting technology into human language presented many difficulties. The probes needed to be thicker to prevent breaking in dense tissue. Even in motion, human brains twitch a little, so researchers had to create software to detect individual neuron signals as they slid over nearby sensors due to the brain’s movement.

To conclude, as the technological obstacles decrease and curiosity about Neuropixels rises, researchers may be able to use these instruments to comprehend a wide range of facets of human existence. Paulk says, “Stay tuned in this space.”

Read the original articl on: Nature

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