Having just concluded perhaps the first formal (i.e., well-
controlled) ethological analysis of rough-and-tumble play in the
human species in the late 1990s, where laughter was an abundant
response, I had the “insight” (perhaps delusion) that our 50-kHz
chirping response in playing rats might have some ancestral
relationship to human laughter. The morning after, I came to the
lab and asked my undergraduate assistant at the time to “come
tickle some rats with me.” Over the ensuing years Panksepp and
his research assistants systematically conducted study after
study on rat laughter, revealing a striking overlap between the
functional and expressive characteristics of this chirping
response in young rodents and laughter in young human children.
To elicit laughter in his rat pups, Panksepp used a technique
that he called “heterospecific hand play,” which is essentially
just jargon for tickling. Rats are particularly ticklish, it
seems, in their nape area, which is also where juveniles target
their own play activit