Beyond 22 and 50 kHz: Revisiting the third category of rat ultrasonic vocalizations

Adult rats are known to produce two categories of ultrasonic vocalizations (USVs): 50-kHz and 22-kHz calls. The former are typically associated with positive emotional states and social approach, whereas the latter are linked to negative states such as warning, anxiety, and fear. However, recent studies have suggested the existence of a “third category” of USVs, characterized by intermediate frequency (30–45 kHz) and duration. The behavioral contexts of these vocalizations are diverse and inconsistent, including extreme stress (Olszyński et al., 2024), social isolation and inequity (Okabe et al., 2023), and feeding (Champeil-Potokar et al., 2023). It remains unclear whether these USVs reflect motor “errors” in producing 50- or 22-kHz calls, or represent distinct emotional or motivational states. In this presentation, we review these findings and discuss possible interpretations. We also introduce our lab’s ongoing efforts using a novel recording system to track vocalizing individuals, in order to investigate whether rat vocalizations exhibit individual variation or vocal signatures.