The newly discovered circuit controls two critical aspects of vocalization: contraction of the larynx (vocal cords) and exhalation of air. This circuit works under the control of a region in the brainstem that provides breathing priority by regulating the breathing rhythm.
“Vocalization has to stop when you need to breathe,” explains Fan Wang, the study’s senior author and a professor at the Massachusetts Institute of Technology. “We found that neurons controlling vocalization receive inhibitory signals from the respiratory rhythm generator.”
The vocal cords are located in the larynx and open and close to produce sound. When they are partially closed, the exhaled air passing through them creates sound. Researchers used mice that communicate using ultrasonic sounds to understand how the brain controls sounds. They focused on how the brain controls the closure of the vocal cords and how these neurons interact with the respiratory circuit.
By mapping neural connections, researchers identified a group of premotor neurons in the hindbrain called RAm (retroambiguus nucleus). Previous studies have linked this region to vocalization, but the specific role and mechanism were unclear. The researchers observed that these RAm neurons, called RAmVOCs, were highly active during the mice’s vocalizations. Subsequent research confirmed their critical role. Further analysis showed that the pre-Bötzinger complex, a brainstem region responsible for generating the inspiratory rhythm, directly inhibited RAmVOC neurons. This allows breathing to be prioritized during speech, forcing us to pause to take a breath while speaking.
Although human speech is much more complex than mouse vocalizations, the researchers believe the discovered circuit plays a similar role in the production of human speech. Future research will investigate how the brain circuits that control breathing and vocalization may affect other functions, such as coughing and swallowing.
Source: Ferra
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