Modulation of Breath Airflow Patterns Generates Diverse Vocalizations in Mice

Core Concepts

The modulation of breath airflow patterns, controlled by the intermediate Reticular Oscillator (iRO) in the brainstem, is a key mechanism for generating diverse vocalizations in mice.

Abstract

The study investigates the mechanisms underlying the production of diverse vocalizations in mice, focusing on the role of breath airflow patterns and the brainstem vocalization central pattern generator, the iRO.

Key highlights:

• Vocalizations in mice are produced within normal breathing cycles, with the vocalization sounds nested within the expiratory phase.
• Two distinct mechanisms modulate the pitch of vocalizations: 1) positive intonation, where pitch changes correlate with changes in expiratory airflow, and 2) negative intonation, where pitch changes anticorrelate with airflow.
• The activity of inspiratory and laryngeal muscles is coordinated to produce these two intonation patterns, with ectopic activation of this breathing-related muscle activity observed during vocalizations.
• The iRO, a brainstem vocalization central pattern generator identified in neonatal mice, is also present in adults and is sufficient to induce most of the diverse vocalization types in the mouse repertoire by modulating the breath airflow.
• These findings reveal a novel brainstem mechanism for generating vocal intonation and demonstrate the crucial role of the iRO in shaping the adult mouse vocal repertoire.

Stats

"The instantaneous frequency of vocalization breaths was typically between 5-10 Hz (mean: 7.5 Hz)."
"Vocalization breaths were slightly slower overall with subtly larger inspiratory and perhaps expiratory airflow despite similar durations of each phase."
"Five of the ten USV syllable types had positively shifted intonation, the complex, step down, chevron, two step, and multi."
"The up fm was the only USV with negative intonation."

Quotes

"Ectopic activation of the inspiratory and laryngeal muscles appears to result in a USV with positive intonation and the cyclic engagement of this leads to an oscillating pitch."
"The novel finding that the endogenous pattern of the breathing CPG is re-engaged within an adult vocal breath, a 'mini-breath', mimics the rhythmic syllables of the neonatal vocalizations patterned by the intermediate Reticular Oscillator (iRO)."
"Ectopic excitation of the iRO produces seven of the ten syllable types within the murine lexicon."

Key Insights Distilled From

The breath shape controls intonation of mouse vocalizations

by MacDonald,A.... at www.biorxiv.org 10-17-2023

https://www.biorxiv.org/content/10.1101/2023.10.16.562597v2

Deeper Inquiries

How do the two distinct intonation mechanisms (positive and negative) interact to produce the full diversity of vocalizations in mice?

The two distinct intonation mechanisms, positive and negative, interact to produce the full diversity of vocalizations in mice by modulating the breath airflow and laryngeal opening. Positive intonation involves changes in pitch that positively correlate with the breath expiratory airflow, while negative intonation involves changes in pitch that negatively correlate with the laryngeal opening. These mechanisms can work independently or in conjunction within a single breath to create a diverse repertoire of vocalizations. The positive intonation mechanism, controlled by the iRO, patterns the vocalizations by coordinating the breath airflow and laryngeal muscle activity. On the other hand, the negative intonation mechanism, likely controlled by laryngeal premotor neurons in the RAm, dictates the anti-correlated USV types. The interplay between these two mechanisms within a single breath allows for the creation of various pitch patterns and vocalizations in mice.

How do the specific neural circuits and signaling pathways link the iRO to the laryngeal motor control and breathing pacemaker systems?

The specific neural circuits and signaling pathways linking the iRO to the laryngeal motor control and breathing pacemaker systems involve the iRO neurons projecting to key areas responsible for vocalization. The iRO, identified by the co-expression of Penk and Vglut2, is anatomically localized in the medullary ventral intermediate Reticular Formation (iRT) adjacent to the compact nucleus ambiguus (cNA). The iRO neurons send axons to the nucleus ambiguus (NA) and retroambiguus (RAm), where laryngeal premotor and motor neurons are located. Additionally, the iRO neurons project to the breathing pacemaker, the preBötzinger Complex (preBötC), and the hypoglossal motor nucleus. These connections allow the iRO to control both the breath airflow and laryngeal opening, essential for producing vocalizations. Furthermore, the iRO receives input from the midbrain periaqueductal gray (PAG), a region implicated in vocalization initiation, suggesting a hierarchical pathway from PAG to iRO to the laryngeal motor control and breathing pacemaker systems.

Could the principles of vocal intonation control revealed in mice be generalized to other mammalian species, including humans?

The principles of vocal intonation control revealed in mice, particularly the role of the iRO in modulating breath airflow and laryngeal muscle activity to produce diverse vocalizations, could potentially be generalized to other mammalian species, including humans. While there may be species-specific variations in the neural circuits and mechanisms involved in vocalization, the fundamental principles of intonation control through coordinated changes in breath airflow and laryngeal control are likely to be conserved across species. The identification of the iRO as a central component of the brainstem phonation circuit in mice suggests a common mechanism for intonation regulation in mammals. Further research in humans and other species is needed to fully understand the extent of generalizability of these principles across different mammalian vocalization systems.