Researchers have pinpointed a brain circuit in rats that fires when the animals are tickled.
Rats are known to chirp or 'laugh' when tickled. To find the neural mechanism, Michael Brecht and Shimpei Ishiyama at the Humboldt University of Berlin inserted electrodes into the somatosensory area of the rat brain, which responds to touch on the skin. Certain neurons in this region fired intensely when the rats were tickled on their bellies, but responded less to back-tickling and hardly at all to tail-tickling.
By stimulating these neurons with the electrodes, the researchers caused the rats to chirp in the same way they do when tickled.