Why are these scientists tickling rats?

Believe it or not, tickling rats has become a thing in science. It started back in the year 2000 when two researchers at Bowling Green State University in Ohio asked the question of whether a “tickling-type somatosensory stimulation by a human hand” was something that rats actually liked.

It turns out the answer is yes. Which is not surprising, but it opened the veritable floodgates of experimentation, nevertheless, primarily due to the scientific interest in the idea of positive affect — or good feelings in layman’s terms — in animals like rats as something that could be measured as well as used to decrease stress and habituate the animal to human contact.

Further, since positive emotions are known to be connected to a range of good health consequences in humans such as resilience to depression and anxiety, having a positive affect marker for one of the top experimental tools in science (the rat) was thought to be beneficial for future experimentation.

On that note, scientists have determined that tickling makes rats … okay, we won’t say laugh, because who knows, but they regularly make sounds when tickled, so much so that scientists have drawn the link between rat vocalizations of the tickling variety (which occur in the 50-kHz range) and positive affect in the animal — and thus, the rationale goes, if and when another event/experiment occurs that produces similar vocalizations, experimenters can be moderately assured that the rat is happy as a result.

Now, before going any further, you should probably go look at a few clips of scientists tickling rats and see how that ups your own positive affect.

Thus, with all this rat tickling for science going on, you might think that a good, standard protocol would have been developed as to: (a) the best technique to use to tickle and (b) the common outcomes from the tickling to be measured. Yet, neither have been established, a deficit, say the authors of a new study entitled, “Rat tickling: a systematic review of applications, outcomes and moderators.”

“Rat tickling is a promising habituation technique that can also be used to model and measure positive affect,” say the authors, who include researchers from Purdue University in West Lafayette, Indiana, and the Canadian Council on Animal Care in Ottawa, Ontario. “However, current studies use a variety of methods to achieve differential results.”

To that end, the researchers looked at 32 articles involving 56 different experiments on rat tickling published in peer-reviewed journals and compared methods and outcomes. While they found a wide range of approaches being used, the most common one came from the pioneering study in 2000, namely, a “dorsal contact” on the rat’s neck accompanied by a “pin” on the rat’s stomach (try that on your significant other), cycled through 15 seconds of tickling followed by 15 seconds of rest for 2-minute stretches. Along with vocalization, the researchers found that experiments commonly looked at behaviours such as approach (coming back to the tickling hand), anxiety and fear behaviours, hormonal effects and even genetic and cellular level effects of tickling.

In all, the researchers found that the studies under review showed evidence of many positive effects of tickling rats along these outcome measures but stressed that a common protocol is still wanting and that future research is needed to determine the “ideal dosage of tickling” in order to standardize the practice. “We conclude that tickling is a promising method for improving rat welfare and investigating positive affect,” say the authors. “However, the establishment of tickling best practices is essential as the outcomes from tickling can be moderated by several factors.”

The new research is published in the journal PlosOne.

Below: What happens when you tickle a rat?