The Secret Life of Tickling

One of my daughters is so ticklish, I can tickle her without even touching her. I dramatically wiggle my hands over her and it’s all over—she’s helplessly squealing with delight. Tickling is indeed a mysterious phenomenon. It’s one long studied by scientists and psychologists, and even Charles Darwin got into the field of tickle research, coming up with his Darwin-Hecker hypothesis linking humor and tickling. So the silly stuff can apparently produce serious subjects. Now, new research with rats has added to the giggling body of knowledge.

A new study looked at how young rats respond when tickled by humans. You are probably wondering, how can you tell if a rat is ticklish? They emit a “laughtercall” sound, often perform a “joy jump”, and playfully respond to the researcher’s hand. The rats, it turns out, were most ticklish on their bellies and feet—like many humans.

Once the researchers knew where the rats were most ticklish, they looked at the their response to tickling. Researchers observed a strong response in nerve cells of the somatosensory cortex, a large brain structure that handles stimuli on the body. The rats’ brains were behaving, when tickled, the same way their brains do when the rats were playing. An anxious rat is not as ticklish, and also reduces levels of response in the nerve cells of the somatosensory area.

Professor Michael Brecht, of the Bernstein Center for Computational Neuroscience in Berlin, led the study. Dr. Brecht wrote, “The data much look like we identified the ticklish spot in the rat brain. I also find the similarity of brain responses to tickling and play remarkable. Perhaps ticklishness is a trick of the brain that rewards interacting and playing.”

That might explain why we can’t tickle ourselves. There’s no reward, if the point of tickling is to play and engage with others.