Mouse vocal communication system: Are ultrasounds learned or innate?

Mouse ultrasonic vocalizations (USVs) are often used as behavioral readouts of internal states, to measure effects of social and pharmacological manipulations, and for behavioral phenotyping of mouse models for neuropsychiatric and neurodegenerative disorders. However, little is known about the neurobiological mechanisms of rodent USV production. Here we discuss the available data to assess whether male mouse song behavior and the supporting brain circuits resemble those of known vocal non-learning or vocal learning species. Recent neurobiology studies have demonstrated that the mouse USV brain system includes motor cortex and striatal regions, and that the vocal motor cortex sends a direct sparse projection to the brainstem vocal motor nucleus ambiguous, a projection previously thought be unique to humans among mammals. Recent behavioral studies have reported opposing conclusions on mouse vocal plasticity, including vocal ontogeny changes in USVs over early development that might not be explained by innate maturation processes, evidence for and against a role for auditory feedback in developing and maintaining normal mouse USVs, and evidence for and against limited vocal imitation of song pitch. To reconcile these findings, we suggest that the trait of vocal learning may not be dichotomous but encompass a broad spectrum of behavioral and neural traits we call the continuum hypothesis, and that mice possess some of the traits associated with a capacity for limited vocal learning.

Graphical abstractTop panel shows mouse song system connectivity, highlighting the presence of a direct projection from M1 cortex to the vocal motor neurons of nucleus ambiguous (Amb). The bottom panel shows pitch imitation between C57 and BxD male mice over the course of 8 weeks of co-housing in the presence of a female of either strain (conditions 1 and 2).Figure optionsDownload full-size imageDownload high-quality image (58 K)Download as PowerPoint slideHighlights► Mice have forebrain circuits active during singing. ► Mice have a direct motor cortical projection to vocal motor neurons. ► Mice make changes in vocalizations over early development that can not be explained by innate behavior alone. ► Mice have a partial dependence on auditory feedback to maintain acoustic features of their songs, but this is under debate. ► Mice can copy the pitch of another strain’s song as adults.