Differential association of high- and low-frequency rat vocalizations with breathing and locomotion during social interactions.

Rodents, including rats, utilize vocalizations as a primary mode of social communication. While high-frequency ultrasonic vocalizations (USVs) have been extensively explored in laboratory rats, low-frequency (<10 kHz) vocalizations (LFVs) were first described only recently, and it is as yet unclear whether these two types of vocalizations are driven by the same behavioral mechanisms. This study investigates the behavioral distinctions between USVs and LFVs in socially interacting rats. In line with previous studies, we found that USVs, mostly associated with social interactions, are emitted during early stages of exhalation and involve complex respiratory modulations. In contrast, LFVs, which correlate with general arousal, occur early at inhalation, show limited deviation from baseline breathing patterns, and are significantly associated with locomotion. Advanced machine learning models, including long short-term memory convolutional neural network frameworks and semiparametric mixed-effects models, were employed to analyze the interplay between vocalizations, respiration, body orientation and locomotion. The results of these analyses demonstrate that USVs are well predicted by the breathing pattern and are associated with social interaction and orientation toward the social stimulus. In contrast, LFVs were predicted poorly from the breathing pattern alone, but are correlated with both breathing rate and locomotion. Moreover, they shared common dynamics with the power of theta oscillations in the nucleus accumbens core, a brain area associated with motivation and emotions. We conclude that these two vocalization types represent distinct communicative and physiological phenomena. These findings advance the understanding of rodent vocal communication and highlight the possible adaptive roles of LFVs in behavioral contexts.