Introducing the brain: speech and breathing controls (Introduction)

by David Turell , Thursday, March 07, 2024, 20:36 (51 days ago) @ David Turell

We breath out to speak:

https://medicalxpress.com/news/2024-03-brain.html

"The newly discovered circuit controls two actions that are required for vocalization: narrowing of the larynx and exhaling air from the lungs. The researchers also found that this vocalization circuit is under the command of a brainstem region that regulates the breathing rhythm, which ensures that breathing remains dominant over speech.

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"They knew that vocal cord adduction is controlled by laryngeal motor neurons, so they began by tracing backward to find the neurons that innervate those motor neurons.

"This revealed that one major source of input is a group of premotor neurons found in the hindbrain region called the retroambiguus nucleus (RAm). Previous studies have shown that this area is involved in vocalization, but it wasn't known exactly which part of the RAm was required or how it enabled sound production.

"The researchers found that these synaptic tracing-labeled RAm neurons were strongly activated during USVs [mouse ultrasonic vocalizations]. This observation prompted the team to use an activity-dependent method to target these vocalization-specific RAm neurons, termed as RAmVOC.

"When the researchers blocked the RAmVOC neurons, the mice were no longer able to produce USVs or any other kind of vocalization. Their vocal cords did not close, and their abdominal muscles did not contract, as they normally do during exhalation for vocalization.

"Conversely, when the RAmVOC neurons were activated, the vocal cords closed, the mice exhaled, and USVs were produced. However, if the stimulation lasted two seconds or longer, these USVs would be interrupted by inhalations, suggesting that the process is under control of the same part of the brain that regulates breathing.

"'Breathing is a survival need," Wang says. "Even though these neurons are sufficient to elicit vocalization, they are under the control of breathing, which can override our optogenetic stimulation."

"Additional synaptic mapping revealed that neurons in a part of the brainstem called the pre-Bötzinger complex, which acts as a rhythm generator for inhalation, provide direct inhibitory input to the RAmVOC neurons.

"'The pre-Bötzinger complex generates inhalation rhythms automatically and continuously, and the inhibitory neurons in that region project to these vocalization premotor neurons and essentially can shut them down," Wang says.

"This ensures that breathing remains dominant over speech production, and that we have to pause to breathe while speaking.

"The researchers believe that although human speech production is more complex than mouse vocalization, the circuit they identified in mice plays the conserved role in speech production and breathing in humans."

Comment: breathing is so important there had to be a mechanism to control both. All animals are generally vocal. It is a necessary attribute: alarm, pay attention to me, hello, etc.