Researchers discovered that rats emit ultrasonic giggles when tickled, now known as “joy jumps.” Curiously, the only rats that enjoyed being tickled were those in a good mood.
The study was performed to understand the brain region where excitability and laughter are located, specifically, those related to the effects of tickling, but the research team also discovered the region in the brain that registers activity in touch-sensitive areas.
Lead researchers Shimpei Ishiyama and Michael Brecht from Berlin’s Humboldt University managed to record how rats jump out of joy when tickled. In the process, they emitted giggles in very high pitches, making them inaudible to humans. Previous findings had determined that tickling is a rewarding mechanism, which led the rats to approach the tickling hand after the first round of giggles. The ultrasonic giggles were in a frequency of 50-kHz, similar to that of fluorescent lights.
Furthermore, when the rats were found in anxiety-inducing situations, the nerve cells that activate the somatosensory cortex, which is linked to the rat’s belly, were unable to be tickled any further. It was also discovered that tickling has a correlation to playing behaviors, perhaps in the form of a neuronal link.
After the rat was tickled and its brain activity recorded, the researcher would play with the rat using its hand. The electrode then picked up a brain response very similar to the one of tickling.
To analyze the brain signals, researchers implanted electrodes on the rats’ brains to measure any response related to tickling. When having the electrode inserted, the rats did not appear to have an altered state of mind, which gave the researchers confidence to proceed.
The science of tickles
Because tickling has remained alongside humans throughout evolution, it was considered necessary to determine exactly why mammals enjoy being tickled and why the response ceases to be the same in anxiety-inducing situations. What’s more is that not every part of the body is ticklish and one cannot tickle oneself, a question first raised by the Greek philosopher Aristotle.
The brain activity of the rats when being tickled was considered to be very similar to a human’s. This is also true for ticklish areas, seeing that rats can be tickled on their belly and the soles of their hind legs, which could be equivalent to the plant of our feet.
Dr. Brecht hypothesized that tickling may be linked to play responses because mammals must interact with members akin to its family and species. Tickling would be a well-received response caused by external stimuli in sensitive body parts. Charles Darwin theorized that tickling had to relate with social interaction, as it causes laughter and laughing is a pleasant act. If a stranger were to tickle someone by surprise, oftentimes the result is not laughter but displeasure.
Psychology, on the other hand, affirms that tickling is an important bodily response for parents to interact with their children. At an early age, the pleasure of being touched by one’s parents in the form of tickling would serve as a comparison mechanism for unpleasant situations that may develop, such as the treating of an injury or the concern of being physically harmed.