New paper: Rat ultrasonic vocalizations and novelty-induced social and non-social investigation behavior in a seminatural environment

Rat ultrasonic vocalizations, or USVs, occur at two different frequency ranges. The 22-kHz calls are often produced in aversive situation and are believed to act as warning signals, whereas the 50-kHz calls are considered positive calls and are emitted before, during and after pleasurable events such as sexual or social behavior. Whether those vocalizations have any purpose, and if so, which purpose that is, is not yet clear.  Some studies have suggested that the 50-kHz calls have a function in communication, because they found that rats approach the playback of recordings of these calls. In our laboratory, however, we have not been able to replicate these findings.

In our latest study, we hypothesized that if these USVs are indeed used as means of communication in social behavior, it would be most visible during the first encounters with unfamiliar rats. We therefore performed surgery (devocalization) in one group of rats to disable them from making USVs. If USVs are important during social interactions, we expected that the silent rats would behave differently from another group of vocalizing rats. We tested their behavior in a seminatural environment in which rats can freely move around and socially interact with each other in groups of 7 rats consisting of both silent and vocalizing rats.

We found that during the first hour in the seminatural environment, being unable to vocalize did not change their behavior. They were just as quick to meet other rats, showed similar social investigation behavior, passive social behavior or aggressive behavior as their vocalizing group members. Furthermore, the non-social exploratoring behaviors and behaviors reflecting anxiety or stress-like states were also unaffected. These results demonstrated that a disability to vocalize did not result in significant disadvantages (or changes) compared to intact conspecifics regarding social and non-social behaviors. This suggests that USVs might not be very important for communication, and that other (multi)sensory cues (e.g. smell) are more relevant in social interactions than USVs.

This study is part of a collaboration between our group at UiT The Arctic University of Norway and the Norwegian University of Science and Technology.

[Summary by Eelke]

Indrek Heinla, Xi Chu, Anders Ågmo, Eelke Snoeren. (2021) Rat ultrasonic vocalizations and novelty-induced social and non-social investigation behavior in a seminatural environment. Physiology and Behavior. doi: 10.1016/j.physbeh.2021.113450