Rats love to be tickled and they not only "giggle" but they jump for joy, too, researchers reported Thursday.
And they'll chase your hand begging for another tickle, the team at the Humboldt University of Berlin in Germany reported.
What's the point of tickling rats for science? Neuroscientist Shimpei Ishiyama and colleagues said they were answering important questions.
"Why does tickling induce laughter? Why are tickling effects so mood-dependent? Why do body parts differ in ticklishness? Why can't we tickle ourselves? Is ticklish laughter different from humorous laughter?" they wrote in their study, published in the journal Science.
"To address such questions, we need a better understanding of the neural correlates of ticklishness." In other words, where in the brain is our tickle center?
Brain scans have suggested that in people, it's the somatic sensory cortex, a cluster of centers on the top outside part of the brain where humans process touch sensation.
So Ishiyama's team implanted electrodes in the same region of the rats' brains, and then tickled them.
"We tickled and gently touched rats on different body parts and observed a variety of ultrasonic vocalizations," they wrote. Other studies have shown these are the equivalent of very high-pitched rat giggles.
"We confirmed that tickling of rats evoked vocalizations, approach and unsolicited jumps (Freudensprünge)," they wrote. Freudensprünge translates roughly to jumping for joy.
And the same area of the rat brains work as in humans. "We found that tickling can evoke intense neuronal activity in the somatosensory cortex," Ishiyama and colleagues wrote.
Not every time, however. When they made the rats anxious by putting them under bright lights or on platforms, the rats did not wriggle and jump and giggle when tickled.
So what does it all mean?
"The observation that the somatosensory cortex is involved in the generation of tickling responses suggests that this area might be more closely involved in emotional processing than previously thought," the researchers said.
So, just maybe, your affectionate response to someone who knows just how to gently stroke that sensitive part of your neck might all be in your head. Literally speaking, of course.