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Chuckling about that artfully hidden whoopee cushion on your colleague's chair? You may be showing your deep, Darwinian connection to that lovable, jolly, whimsical mammalian relative, the rat.
Jaak Panksepp, the emeritus Bowling Green State University professor who's spent a career demonstrating that animals have an emotional life, is breeding a pack of rats with a sense of humor - or, perhaps more accurately, with a robust giggling response to tickling.
While it's no great surprise that young primates such as chimpanzees and gorillas will giggle when tickled and make laughter-like sounds during play, our appreciation of a good - or not so good - April Fool's prank may have roots far deeper in evolutionary history, Mr. Panksepp's work suggests. In research conducted by Jeff Burgdorf, a doctoral candidate working in Mr. Panksepp's lab, it's becoming clear that the neural circuitry of laughter is interwoven with neural networks that emerged in mammals long before apes swung from the evolutionary tree. In fact, rat laughter has its home in the same part of the brain where rats - and humans - experience reward, the same neural system where drug addictions take devastating hold.
In an essay in today's issue of the journal Science - and soon to appear in the French newspaper Le Monde - Mr. Panksepp writes "although no one has investigated the possibility of rat humor, if it exists, it is likely to be heavily laced with slapstick."
But other than the tongue-in-cheek reference to rat slapstick, Mr. Panksepp seriously contends that his search for the neural circuitry and genes for laughter are a study of "the biology of joy."
His search began about eight years ago when a student in his lab, Brian Knutson, eavesdropped on rats using a device that could pick up their high-pitched chatter. The student noticed the rats chirped vigorously during play. Mr. Panksepp wanted to hear what the rats would do when tickled, so he and Mr. Burgdorf began one of the few - although not the only - tickling experiments in the annals of science.
The BGSU researchers efforts revealed that rats giggle even more during tickling than they do in play. In fact, researchers uncovered a "kootchie-coo phenomenon" in previously tickled rats. Just as a child will giggle if he thinks he's about to be tickled, so will rats. The experimenter needed only to fake a tickle, and the rats cracked up.
Researchers noted that rats housed alone readily bonded to the gloved hand that tickled them. In one set of experiments, one person petted rats, and another person tickled the same rats. When rats were presented with the hand of each person, "they ran for the tickle hand,'' Mr. Panksepp said. "Like a cat, or especially a dog, they stay close to you, and they follow you around, you have them chasing your hand like a pied piper."
If the tickling hand was first squiggled around in something that smells interesting, such as coffee grounds, "the animal later treats coffee as a positive thing in the environment," he said.
In an attempt to tease out the genetic roots of laughter, the researcher is breeding rats that show the greatest propensity for ticklish laughter with other light-hearted rodents. Conversely, he's also breeding slow-to-chuckle rats with similarly solemn mates. So far, 10 generations of breeding have resulted in one brood of rats that chirps easily, and another that's reluctant to do so. Further testing will be required to be certain the chirping differences are actually a response to play, and not a sign of some motor differences - a paralysis in the throat, for instance, in the laughless rats.
Ultimately, as rat breeding continues along these lines, Mr. Panksepp hopes to find the genes most closely connected to laughter.
"People say, how could you waste your time on that? I say, this is one of the most important discoveries of the 20th century. There are 10,000 people studying memory and learning and one guy studying the biology of joy. Understanding the biology of emotions is just as important as understanding cognition.''
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