Researcher are always looking for ways to improve the accuracy of their findings, and one of these ways is to ensure that they know about each and every factor that can influence a lab subject. Now, a new study has found that to ensure that lab rats are not too stressed after feeling the bite of a hypodermic needle, you simply have to tickle them.

The fact that mice are ticklish and take the same kind of joy out of the experience that humans do is not exactly new news.

The Laughing Rats

Back in the late 1990s, neuroscientist Jaak Panksepp discovered that as lab rats played with one another, they emitted unique ultrasonic chirps that were associated with a positive emotional state. Panksepp and his colleagues quickly came to the conclusion that these chirps could only best be described as laughter, and if rats could laugh, was is possible that they could be ticklish too?

Back in 2000, the October issue of the journal Behavioral Brain Research detailed a study that investigated just that, with Panksepp and Jeffery Burgdorf at the J.P. Scott Center for Neuroscience, Mind and Behavior, at Bowling Green State University, slipping on their doctors' gloves to administer some "playful, experimenter-administered manual stimulation."

This stimulation - you or I would call it "tickling" - was performed in a very specific way for the sake of consistency. According to Panksepp, the only scientific way to tickle a rat is done with the right hand.

"The tickling... consisted of rapid initial finger movements across the back with a focus on the neck, followed by rapidly turning the animals over on their backs, with vigorous tickling of their ventral surface (belly), followed by release after a few seconds of stimulation," the researchers wrote. "This was repeated throughout each tickling session. Even though the tickling was brisk and assertive, care was taken not to frighten the animals."

Amazingly, these tickling sessions always induced that tiny rodent laughter, and the researchers started to organize their rats based on who seemed to enjoy tickling the most and laugh the hardest. (Scroll to read on...)

They then bred four generations of these rats, specifically selecting for high and low tickling responses.

"The high tickle line showed quicker acquisition of an instrumental task for, as well as less avoidance of, tickling as compared to the random and low tickle lines," Panksepp observed.

Additionally, the ticklish and hearty laughers played more.

Well, Tickle Me Optimistic

Then, in 2012, a new study published in the journal PLOS One provided evidence that tickling not only made these rats laugh, but made them optimistic as well.

For this study, a large group of rats were taught to listen to one of two tones, press a lever, and then either receive a mild electric shock or a tasty treat. They quickly learned to press the lever only when hearing the tone for food, and avoided the lever when the shock-associated tone was played.

However, when a new and ambiguous tone was played, the rats were suddenly given a choice: risk the lever, or play it safe?

Amazingly, the researchers found that rats who were tickled right before being presented with this choice were far more likely to take the risk, compared to rats who were simply handled before choice time.

The study's authors suggested that the tickled rats were put in a better mood by the tickling, prompting them to be more optimistic about the tone. This also provided the first solid evidence that tickling could influence a rat's behavior.

A Behavioral Balancing Act

So what exactly did that discovery mean for science? For one, it added one more factor to the ever-mounting list of lab animal influences.

New research has shown that rats are not actually superior to mice for behavioral and neural studies, with both animals capable of complex cognitive tasks and expressing varied personalities. Past studies have also revealed that male rats and mice often grow nervous after smelling male researchers - their stress levels potentially skewing chemical and behavioral data. (Scroll to read on...)

And this revelation has caused researchers to worry that stressful stimuli, such as the prick of a needle during a necessary injection, can put these animals into a state of mind that could influence their behavior.

That's where laughter gets to prove itself as the best medicine.

A study published just this year in the journal Applied Animal Behavior Science has found that although tickling can indeed influence rat behavior, it can also serve as a powerful tool in preventing more adverse influences.

"We hypothesized that administering playful tickles before and/or after routine... injections would reduce the aversiveness of such medical procedures," co-author Sylvie Cloutier, from Washington State University, wrote in the study.

To test this, she and her colleagues tickled some rats before, and others after regular saline injections. A third injection group was unlucky enough to receive no tickling. They then compared the levels of discomfort felt by each rat during the procedure, measuring how much they fought their restraints, and how frequently they audibly complained.

Interestingly, the researchers found that rats may be best off if tickled right before an injection, as the good mood from tickling "had a carry-over effect" that counteracted the "negative states" that the saline injection could put the rats in.

That is to say that tickling a rat right before injection helped it say "this isn't so bad" during and right after a procedure.

So tickle your rats, scientists! Your data tables (and rats) will thank you.

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