Rodents emit ultrasonic vocalizations (USV) of different frequencies in order to communicate. We study their general relevance to behavioral neuroscience. The relationship between behavior and USVs as well as neurophysiology and USVs attracts increasing scientific attention as they give important insights about the affective state of the subject while doing a certain task. However, these vocalizations appear in a frequency range, which cannot be heard with the human ear, and new modern technical equipment is used to record such vocalizations.
Dependent on sound frequency and call length three different classes of USVs can be identified in rats.
Rat pups typically emit USV around 40-kHz (Fig. 1a) in response to distress situations, e.g. when being separated from their mother. These isolation induced anxiety calls of pups represent the negative affective state and can be attenuated with the administration of anxiolytic drugs, such as benzodiazepine. However, these calls also have a communicative function, as they help the mother to localize the pup and bring it back to the litter.
Juvenile and adult rats produce two different types of calls the 22-kHz and 50-kHz USVs. Their occurrence depends on the physical and psychological demands of the environment. The 22-kHz (figure 2) low frequency vocalizations are emitted in aversive situation, when exposed to predators. They represent a negative affective state akin to anxiety and depression. Further studies suggest that they serve as an ‘alarm call’ in order to warn conspecifics about a danger (e.g. a cat). Other playback studies have also shown that animals respond to 22 kHz calls with freezing.
In appetitive situations such as in response to reward, mating and rough and tumble play rats exhibit the high-frequency 50 kHz USVs (figure 3). It is assumed that these calls reflect a positive affective state akin joy. Further, they promote and maintain rough and tumble play in juvenile rats. Interestingly, rats when being tickled also emit this 50 kHz calls. Therefor it is suggested that these 50 kHz vocalizations are a precursor of human
Literature:
Rippberger, H., van Gaalen, M.M., Schwarting, R.K.W. and Wöhr, M. (2015). Environmental and Pharmacological Modulation of Amphetamine- Induced 50-kHz Ultrasonic Vocalizations in Rats. Current Neuropharmacology 13: 220. https://doi.org/10.2174/1570159X1302150525124408
Seffer, D., Schwarting, R. K., & Woehr, M. (2014). Pro-social ultrasonic communication in rats: insights from playback studies. Journal of neuroscience methods, 234, 73-81.
Wöhr, M., & Schwarting, R. K. (2013). Affective communication in rodents: ultrasonic vocalizations as a tool for research on emotion and motivation. Cell and tissue research, 354(1), 81-97.
