Maternal approaches to pup ultrasonic vocalizations produced by a nanocrystalline silicon thermo-acoustic emitter.

When infant rodents are isolated from their mother and littermates, they cool rapidly and emit ultrasonic vocalizations (USVs). The effect of pup USVs on the mother has been investigated using models of pup USVs from ultrasonic speakers. We used a nanocrystalline silicon thermo-acoustic emitter (nc-Si emitter) to investigate mothers' responses to digitally reproduced pup USVs in mice. The nc-Si emitter could reproduce ultrasonic sounds more accurately than conventional emitters. We compared the sound properties of pup USVs and reproduced USVs. We then investigated maternal responses to hypothermic pups, which emit USVs, and anesthetized pups, which are silent, as well as maternal responses to pup USVs reproduced by the nc-Si emitter and a silent mode. The nc-Si emitter can reproduce pup USVs very accurately in terms of duration, frequency, and sound pressure level. Mothers approached reproduced digitally recorded pup USVs from the nc-Si emitter and their behavior was similar to their behavior toward hypothermic pups. In contrast, mothers did not approach other synthesized ultrasounds, such as double-duration USVs, double-silence domain ultrasounds nor double-ultrasonic domain ultrasounds, indicating that they approach the specific profiles of pup USVs. These results indicate that the nc-Si emitter can be useful to elucidate the role of ultrasonic acoustic communication in rodents.