Ultrasonic communication in rats: appetitive 50-kHz ultrasonic vocalizations as social contact calls

Rats are highly social animals, with a rich social behavioral repertoire, including the emission of so-called ultrasonic vocalizations (USV). Typically, three main types of USV can be distinguished based on a number of acoustic features, such as call duration, peak frequency, and frequency modulation: (I) isolation-induced 40-kHz USV in pups, as well as (II) aversive 22-kHz USVand (III) appetitive 50-kHz USVin juvenile and adult rats. In this review, evidence from selective breeding, devocalization, and playback studies is summarized and discussed, and it is concluded that appetitive 50-kHz USV serve as situation-dependent socio-affective signals with important communicative functions, for instance as play signals and/or social contact calls.