Translating mouse vocalizations: prosody and frequency modulation

Abstract

Mental illness can include impaired abilities to express emotions or respond to the emotions of others. Speech provides a mechanism for expressing emotions, by both what words are spoken and by the melody or intonation of speech (prosody). Through the perception of variations in prosody, an individual can detect changes in another's emotional state. Prosodic features of mouse ultrasonic vocalizations (USVs), indicated by changes in frequency and amplitude, also convey information. Dams retrieve pups that emit separation calls, females approach males emitting solicitous calls, and mice can become fearful of a cue associated with the vocalizations of a distressed conspecific. Because acoustic features of mouse USVs respond to drugs and genetic manipulations that influence reward circuits, USV analysis can be employed to examine how genes influence social motivation, affect regulation, and communication. The purpose of this review is to discuss how genetic and developmental factors influence aspects of the mouse vocal repertoire and how mice respond to the vocalizations of their conspecifics. To generate falsifiable hypotheses about the emotional content of particular calls, this review addresses USV analysis within the framework of affective neuroscience (e.g. measures of motivated behavior such as conditioned place preference tests, brain activity and systemic physiology). Suggested future studies include employment of an expanded array of physiological and statistical approaches to identify the salient acoustic features of mouse vocalizations. We are particularly interested in rearing environments that incorporate sufficient spatial and temporal complexity to familiarize developing mice with a broader array of affective states.

Figure 1

Spectrograms of call sequences differ among mice of varied ages and social contexts. Pup separation calls were collected from an 8-day-old mouse of the C57BL/6J strain approximately 1 minute after removal from the nest and placement in a soundproof chamber at 23 °C. Wriggling calls were recorded from pups within the litter of the C57BL/6J strain approximately 1 minute after placing the microphone above the nest. Juvenile calls were recorded approximately 30 seconds after two male C57BL/6J mice (PD30) were reunited in a home cage environment after 24 hours of social isolation. Calls emitted during female-female interactions were collected approximately 20 seconds after an intruder female was inserted into the cage of a resident female, both mice of the C57BL/6J strain after 3 days of social isolation. Calls emitted during male-female interactions were collected approximately 20 seconds after an adult female of the C57BL/6J strain was inserted into the cage of an adult male mouse of the C57BL/6J strain in his home cage environment. Calls emitted during male-male interactions were collected approximately 20 seconds after an intruder male of the C57BL/6J strain was inserted into the cage of a resident male mouse of the C57BL/6J strain in his home cage environment after 3 days of social isolation.

Figure 2

Spectrograms of representative call types emitted by juvenile male C57BL/6J mice (P30) mice reunited in a home cage environment after 24 hours of social isolation. Spectrograms include examples of an upward-modulated call (A), down-ward modulated call (B), chevron (C), complex call (D), and punctuated call (E). The abrupt change in frequency in figure E is a pitch jump (p), indicated by the downward pointing arrow (F). Time (in seconds) is indicated by the X axis, frequency in kHZ is indicated by the Y axis, and relative intensity, or loudness is indicated by color (see key).