Adult rat ultrasonic vocalizations (USVs) are commonly classified into 22-kHz and 50-kHz calls, associated with negative and positive emotional contexts, respectively. However, the acoustic features underlying listeners’ responses remain unclear. We examined how mean frequency, call duration, and frequency modulation contribute to physiological and behavioral responses to rat USVs.
Natural USVs and synthetic probe stimuli were presented to rats, and responses were assessed using heart-rate variability (HRV) and speaker-arm stay time in a radial-arm maze. Probe stimuli were generated by swapping mean frequency and/or call duration between positive 50-kHz and negative 22-kHz USVs, while frequency modulation was quantified from the resulting stimuli. Playback of negative 22-kHz USVs significantly increased mean R–R interval, indicating cardiac slowing, whereas positive 50-kHz USVs did not significantly alter HRV indices after correction for multiple comparisons.
Bayesian modeling revealed that mean frequency and call duration independently predicted changes in mean R–R interval, whereas frequency modulation did not explain the tested HRV index. In the behavioral experiment, mean frequency and call duration also independently predicted speaker-arm stay time. These findings indicate that listeners’ responses to rat USVs are shaped primarily by mean frequency and call duration.
Root mean square of successive differences between adjacent NN intervals Standard deviation of normal-to-normal intervals This research was supported by MEXT/JSPS Grant-in-Aid for Scientific Research on Innovative Areas #4903 (Evolinguistics), Grant Number JP17H06380; Grant-in-Aid for JSPS Research Fellow, Grant Number JP18J13784; JSPS KAKENHI Grant-in-Aid for Scientific Research (S), Grant Number JP23H05428; and JSPS KAKENHI Grant-in-Aid for Early-Career Scientists, Grant Number JP25K17215.We thank members of the Okanoya laboratory at the University of Tokyo/Teikyo University for stimulating discussion. Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, Japan Advanced Comprehensive Research Organization, Teikyo University, 2-21-1 Kaga, Itabashi-ku, Tokyo, Japan Correspondence to Yumi Saito or Kazuo Okanoya. The authors declare no competing interests.
All animal experiments were approved by the University of Tokyo Animal Experiment Committee and Bioscience Committee (Approval No. 27 − 8) and were conducted in accordance with the Regulations for Animal Experiments of the University of Tokyo. The study was carried out in compliance with the ARRIVE guidelines. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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