Contribution of the ventral pouch in the production of mouse ultrasonic vocalizations.

Mouse ultrasonic vocalizations (USVs) are of communicative significance and can serve as one of the major tools for behavioral phenotyping in mouse models of neurological disorders with social communication deficits. Understanding and identifying the mechanisms and role of laryngeal structures in generating USVs is crucial to understanding neural control of its production, which is likely dysfunctional in communication disorders. Although mouse USV production is accepted to be a whistle-based phenomenon, the class of whistle is debatable. Contradictory accounts exist on the role of a specific rodent intralaryngeal structure-the ventral pouch (VP), an air-sac-like cavity, and its cartilaginous edge. Also, inconsistencies in the spectral content of fictive USVs and real USVs in models without the VP points us to re-examine the role of the VP. We use an idealized structure, based on previous studies, to simulate a two-dimensional model of the mouse vocalization apparatus with the VP and without the VP. Our simulations were performed using comsol Multiphysics to examine characteristics of vocalizations beyond the peak frequency (f_{p}), like pitch jumps, harmonics, and frequency modulations, important in context-specific USVs. We successfully reproduced some of the crucial aspects of mouse USVs mentioned above, as observed through the spectrograms of simulated fictive USVs. Conclusions about the lack of a role of the mouse VP were previously made in studies primarily examining f_{p}. We investigated the impact of the intralaryngeal cavity and the alar edge on the simulated USV features beyond f_{p}. For the same combinations of parameters, removing the ventral pouch resulted in an alteration of the call characteristics, dramatically removing the variety of calls observed otherwise. Our results thus provide evidence supporting the hole-edge mechanism and the possible role of the VP in mouse USV production.