Wonder what happens when you tickle a rat?
The ‘weirdest job ever’ could tell researchers a lot about human behaviour
A ticklish rat is an adorable sight.
The chubby little rodent darts toward a scientist’s gloved hand, eager for the delightful agony of its next scratch. It emits rapid-fire, ultrasonic “giggles” — chirps so high pitched they’re inaudible to human ears — and dashes around its enclosure in spontaneous leaps that researchers call Freudensprünge, or “joy jumps.” Joy jumps. Really. “It’s the weirdest job ever, tickling rats professionally,” animal physiologist Shimpei Ishiyama told Smithsonian magazine.
Ishiyama and Michael Brecht, a fellow researcher at Humboldt Univer- sity in Berlin, co-authored a new study in the journal Science on what happens when a rat gets tickled.
They learned that a rat enjoys being tickled only when it feels happy and safe. The scientists also pinpointed the ticklish spot in the rat’s brain and discovered that they could induce behaviour like squeaking and joy jumping just by activating that spot.
The results suggest that tickling could be intimately connected to mood — a finding that could have implications far beyond the world of rodent entertainment. It could help neuroscientists explain the brain circuits associated with mood and the influence of positive thinking on human behaviour.
“This is the only deep scientific approach we currently have to understanding the evolutionary sources of our own emotions, which are very important for deepening psychiatric understanding and treatment of affective disorders,” neuroscientist Jaak Panskepp told Popular Science.
It’s evident in Ishiyama’s study that the rats thoroughly enjoy being tick- led. In a video of the experiment, a gray-and-white rat chases after the scientist’s hand so he can gently ruffle its fur. It joy jumps. It emits the chirps that have been associated with prosocial behaviour and expectations of rewards.
And an electrode inserted into the rat’s brain shows that neurons are enthusiastically firing in the somatosensory cortex — a part of the brain thought to process the physical sensation of being tickled. The “eureka moment” came when the researchers used an electric current to artificially stimulate the targeted area of the brain. The rats immediately began to emit their laughter-like chirps.
The study is the first to use brain stimulation to elicit ticklish laughter, according to Scientific American. And it raises a lot of questions about ways rat ticklishness can help us understand human emotions.
“Rats and humans (diverged) maybe100 million years ago,” Brecht said. “But the phenomenon of ticklishness is remarkably similar.”