There are other ticklish animals out there—dogs and chimps, for instance—but rats are the easiest to handle in a laboratory setting. Neuroscientists Michael Brecht and Shimpei Ishiyama of the Bernstein Center for Computational Neuroscience Berlin implanted an array of electrodes into the somatosensory cortices of five rats. They then tickled the rats and recorded the rodents’ ultrasonic chirps, while noting that the neurons in each animal’s somatosensory cortex fired in concert with each chirping “laugh” pattern. When they later stimulated that brain region directly, the researchers found that could induce the same sort of “laughter” by manipulating the brain alone—implying that this region may be the key to ticklishness in rats.
But when they tried to tickle those same rats under more-trying conditions—on an elevated platform, with a bright light offending the nocturnal rodents’ eyes—the rats barely responded to the tickling. This implies a possible link between somatosensory cortex deactivation and fear, the authors wrote. Meanwhile, Brecht said that the next step is figuring out why rats—and humans—cannot tickle themselves. “I think the tickle response is profoundly social,” he told New Scientist. “Aimed at others, not yourself.”