Rat Ticklers Find Ticklishness Has Deep Evolutionary Roots
(p. A12) As Michael Brecht and Shimpei Ishiyama of the Bernstein Center for Computational Neuroscience in Berlin point out in their report, tickling raises many questions. We don't know why it evolved, what purpose it might serve and why only certain body parts are ticklish. And what about that disappointing and confounding truth that all children and scientists must grapple with: You can't tickle yourself.
The researchers were also inspired by earlier studies. " 'Laughing' Rats and the Evolutionary Antecedents of Human Joy?" published in 2003 in Physiology & Behavior, reported that rats would emit ultrasonic calls when tickled. Ultrasound is too high for humans to pick up.
. . .
The scientists found that tickling and play, which involved chasing a researcher's hand, both caused the same ultrasonic calls and the same brain cells to be active. The scientists also stimulated those cells electrically, without any tickling or play, and got the same calls.
And they found that you can't tickle rats when they are not in a good mood, something that is also true of people.
. . .
And the similarity of tickling in rats and humans is, Dr. Brecht said, "amazing." They even have similar areas that are susceptible for unknown reasons, including the soles of their hind feet, but not of their forepaws.
That similarity suggests that tickling is evolutionarily very ancient, going back to the roots of touch as a way to form social bonds in the ancestors of rats and humans.
"Maybe," Dr. Brecht speculated, "ticklishness is a trick of the brain to make animals or humans play or interact in a fun way."
For the full story, see:
(Note: ellipses added.)
(Note: the online version of the story has the date NOV. 10, 2016, and has the title "Oh, for the Joy of a Tickled Rat.")
Ishiyama and Becht's recent report, discussed above, is:
Ishiyama, S., and M. Brecht. "Neural Correlates of Ticklishness in the Rat Somatosensory Cortex." Science 354, no. 6313 (Nov. 11, 2016): 757-60.
The earlier paper mentioned above, is:
Another paper in this line of research, is: