Tickling Rats Pinpoints 'Tickle Center' of Mammalian Brain

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Neuroscientists at the Humboldt University of Berlin pinpointed the "tickle center" of the mammalian brain by tickling rats. Shimpei Ishiyama/ Michael Brech/ Humboldt University of Berlin

The life of a lab rat is not usually pleasant. They are shocked, drugged, sliced, starved and crippled in the name of furthering scientific understanding, but one group of German rats have had the good fortune of becoming the subjects of a study on tickling.

Neuroscientists from Humboldt University in Berlin embarked on the rat tickling experiment to better understand what happens in the mammalian brain when it is being tickled.

The paper, published in the journal Science on November 11, identifies the "tickle center" part of the brain that elicits ultrasonic squeaks—the equivalent of human laughter.

As well as deepening our understanding of the wiring of the mammal brain, the study's findings have implications for human psychology, particularly with regards to the importance of human touch in forming social bonds.

"Rats emit ultrasonic vocalizations in response to tickling by humans," the paper states. "Tickling is rewarding through dopaminergic mechanisms, but the function and neural correlates of ticklishness are unknown.

"The numerous similarities between rat and human ticklishness, such as tickling-evoked vocalizations and anxiogenic modulation, suggest that tickling is a very old and conserved form of social physicality."

When the neurons associated with tickling were artificially stimulated, researchers were able to get the rats to "laugh." Failure to elicit the same response when the rats were placed in anxiety-inducing situations suppressed the cells' firing, suggesting that mood has an effect on this neuronal activity.

Humboldt University researcher Simpei Ishiyama noted this finding fitted a hypothesis that has been held for centuries.

"Even Darwin observed that children tickled by a stranger would rather scream than laugh," Ishiyama said.

Tickling Rats Pinpoints 'Tickle Center' of Mammalian Brain | Tech & Science