Mountable miniature microphones to identify and assign mouse ultrasonic vocalizations
Vocal communication is a major component of animal social behavior. Vocalizations can be learned or innate, and can convey a variety of signals, including territorial limits, the presence of predators, or courtship intent. Mouse ultrasonic vocalizations (USVs) are a promising model in which to study mammalian vocal production circuits. While mouse USVs are innate, mice still show complex vocal behavior, including production of structured song composed of multiple syllable types and the ability to modify their vocal rate and syllable repertoire based on social conditions. Though in courtship interactions male mice produce the majority of the emitted USVs, female mice are capable of emitting USVs. In order to study the underlying mechanisms of vocal production in freely behaving pairs of mice, it is necessary to identify the individual responsible for each syllable in group settings. Previous methods to identify the source of an individual USVs have used high-density microphone arrays and triangulation methods, which involve the use of multiple costly microphones and require implementation of complex computational methods. Here we identified, developed, and used an inexpensive, mountable, ultrasound-sensitive miniature-microphone system to record and identify USVs from individual mice during dual socializing behavior. Our system includes custom circuit boards that can be fitted to individual mice and connected to a variety of existing USV recording systems. We found that these miniature microphones reliably detected mouse USVs, and that a high percentage (90%) of vocalizations could be attributed to a specific animal in a vocalizing pair based on the relative amplitude differences alone. This simple readout method avoids the implementation of complicated triangulation methods. By pairing this method with simultaneous video recording and automated animal body part and identity tracking, we were able to study and describe the broader courtship behavioral landscape, in which USV production is one component. These results offer a promising, low-cost, and simple method that researchers can implement to study the social vocal communication between at least pairs of vocalizing mice.