Amplitude modulation pattern of rat distress vocalisations during fear conditioning

Abstract

In humans, screams have strong amplitude modulations (AM) at 30 to 150 Hz. These AM correspond to the acoustic correlate of perceptual roughness. In bats, distress calls can carry AMs, which elicit heart rate increases in playback experiments. Whether amplitude modulation occurs in fearful vocalisations of other animal species beyond humans and bats remains unknown. Here we analysed the AM pattern of rat's 22-kHz ultrasonic vocalisations emitted in a fear conditioning task. We found that the number of vocalisations decreases during the presentation of conditioned stimuli. We also observed that AMs do occur in rat 22-kHz vocalisations. AMs are stronger during the presentation of conditioned stimuli, and during escape behaviour compared to freezing. Our results suggest that the presence of AMs in vocalisations emitted could reflect the animal's internal state of fear related to avoidance behaviour.

Male rats emit aversive 44-kHz ultrasonic vocalizations during prolonged Pavlovian fear conditioning

“…Such reduction could potentially be attributed to fatigue (as observed in humans, Kitch and Oates, 1994), despair (e.g., as a reaction to the lack of effects from repeated emissions of 22-kHz calls), or both. The reduction in the amplitude of 22-kHz calls during the 10-trial fear conditioning was also recently observed by others (Gonzalez-Palomares et al, 2023).…”

“…In a recent publication during this paper's review process, Gonzalez-Palomares et al (2023), inspired by our current findings, investigated and reported 44-kHz vocalizations following prolonged (10-trial procedure) odor fear conditioning. These calls were observed predominantly during the late ITI, i.e., 8 th -10 th ITI (Gonzalez-Palomares et al, 2023;Fig. S4C; please note 4 th -7 th ITI were not investigated) after the shock presentations (Fig.…”