Judging from research on rat vocalization during tickling researchers hope it may be possible to use call patterns in rats to measure their emotional response to other interactions and understand how best to improve their welfare. In short, recognizing a positive emotional response in animals is an important way to improve their well-being.
Rats emit high frequency vocalizations which, when produced during human-simulated play or ‘tickling’, are thought to be similar to human laughter. Human laughter is complex and when a person is tickled, they may laugh even if they do not find the experience pleasurable. In rats, it has been impossible to know how much any individual rat ‘likes’ the experience because of limitations in method to directly measure their emotional response. In order to ask the question ‘Do rats like to be tickled?’ the researchers used a behavioral test developed at Bristol which provides a sensitive measure of an animal’s individual emotional experience and they compared the data from this test with the animals vocalizations during ‘tickling’.
The researchers found not all rats like to be tickled and that some rats emitted very high numbers of calls whilst others did not, and these calls are directly related with their emotional experience. Rats which emitted the most calls had the highest positive emotional response to tickling but those who did not emit any or few calls did not show a positive response.
The research revealed that the vocalizations made by rats in response to tickling are an accurate reflection of their emotional experience and something which is easy to measure.
The importance of this study
Being able to assess the welfare of animals accurately and objectively is important but is difficult to achieve. Without being able to ask an animal how it feels, researchers must rely on other methods which have their limitations.
Researchers at Bristol have previously shown that the affective bias test used in this study can provide this type of objective measure, but it is highly specialized and time consuming to run so not readily applied in the wider laboratory animal setting. This current research has found that human-simulated play or ‘tickling’ rats can cause a positive emotional state but not for all rats and by recording vocalizations it is possible to quickly identify which animals benefit from this type of enrichment. Future studies can now monitor vocalizations when other types of scenarios are presented to rats.
Journal Reference: Justyna K. Hinchcliffe, Michael Mendl, Emma S.J. Robinson. Rat 50 kHz calls reflect graded tickling-induced positive emotion. Current Biology, 2020; 30 (18): R1034 DOI: 10.1016/j.cub.2020.08.038