Rats get a bad rap as a member of the order of rodents, but these playful and highly intelligent creatures are a lot more fun than they’re given credit for. We know that rats are ticklish, now we know some enjoy being tickled and that they give away their good mood by emitting high-pitched giggles, new research published in the journal Current Biology reveals.
Previous research that wanted to establish why we laugh when tickled looked to ole’ reliable lab rats to assess if the animals could be used to investigate ticklishness. After all, they had to first establish if rats were even ticklish before using them as a focus species analogous to humans. A sufficient amount of rat jostling proved they were but only when they were feeling cheerful, so next was to establish how the act made them feel.
In humans, tickling can be both good and bad; even if you’re not enjoying it you can find yourself laughing and sporting what science calls the Duchenne smile – in these particularly pertinent times, knowns as "smizing" – anyway. The researchers in this new study wanted to establish if there were any markers in rat tickling response that could reliably indicate if they were loving it or hating it.
The above video shows a rat being used for separate research to this study. It can be heard making the 50kHz "laughter" vocalizations which, as they are ultrasonic, have been transduced to a level we can hear.
Researchers at the University of Bristol, UK, got to work tickling rats and listened out for the frequency and pitch of vocalizations they emitted while it was happening. They found some rats made a lot of noise while others stayed silent. Those that were making a racket were emitting ultrasonic 50kHz calls, which previous research has tied to a positive emotional state. The researchers in this study therefore concluded that if a rat exhibits ultrasonic sounds whilst being tickled, that’s a good sign that it’s having a good time. They compare the calls to human laughter and state that rats are more “honest” in their use of giggling and won’t laugh even in discomfort, as sometimes seen in human laughter.
You might wonder why anyone is so concerned about tickling giggling rats, but the research is intended to improve their welfare by acting as a sort of litmus test for rats' emotional state. The researchers hope that rat handlers can check in on the wellbeing of their rats by running a quick tickling test and listening out for giggles. If they stay silent it means something's afoot.
While a charming concept, previous research has questioned if the 50kHz indicator of happiness in rats is a sophisticated enough measure of positive feeling. One study found that the previous experience of rats had an influence on how often they vocalized, and that specific subtypes of these calls are emitted in situations which aren’t necessarily pleasurable for rats. Therefore it's perhaps wise to be mindful of animals' past experiences when quantifying a happy emotional state using a single indicator.