Psychology Ph.D. Dissertations

The Neurobiology of 50-Khz Vocalizations in Rats

Date of Award


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)



First Advisor

Jaak Panksepp


A wide variety of myomorph rodents (e.g., rats and mice) emit ultrasonic vocalization (USVs) in response to a wide variety of social interactions across their lifespan. Many rodents emit ultrasonic vocalizations during infant maternal separation, rough-and-tumble play, aggression, or mating. It has been proposed that rodents utilize ultrasonic vocalizations as communicative signals, given that it is both difficult for predators to hear these calls due to their rapid attenuation across short distance, and the lack of hearing sensitivity for ultrasonic tones of many rodent predators (Nyby & Whitney, 1978). Ultrasonic vocalization production has been most extensively studied in laboratory rats. Recent experiments suggest that rat USVs vary across two independent dimensions – peak frequency that may index locomotor arousal, and frequency modulation which may index emotional valence. In this paper, we hypothesize that high frequency vocalizations (50-70 kHz) are related to high levels of locomotor arousal, whereas lower tones (20-40 kHz) are related to low levels of locomotor arousal often accompanying freezing. We also hypothesize that frequency modulated (FM) vocalizations, which include trill and step calls, reflect a positive affective rewarding state in the animal, whereas non-FM calls (i.e. constant frequency calls) are unrelated to reward and perhaps may reflect aversion. The apparent arousal and valence encoding of ultrasonic vocalizations would presumably allow for rapid, high fidelity decoding by receivers of the motivational and emotional states of senders. Ultrasonic vocalizations may function by evoking the same emotional state of senders in receivers and thereby coordinate social behavior. The relationship between 50-kHz USVs and reward will further be tested by examining the relationship between 50-kHz calls during rough-and-tumble play and the rewarding value of play (Chapter 1A), and the relationship between electrical and chemical brain stimulation induced USVs and the rewarding value of the stimulation (Chapter 2).