Have you ever thought about what rats have in common with comedy club audiences? No? I hadn’t either until I met neuroscientist Jaak Panksepp, a founder of the discipline called affective neuroscience.

Jaak Panksepp, founder of affective neuroscience

Jaak Panksepp with Degu

Professor Panksepp studies the origins of play that lay deep in our evolutionary history by watching rats tussle and by examining their neuroarchitecture and neurochemistry. When a mutual friend introduced us, I reminded Panksepp of the comedian, Henny Youngman, who once quipped, “I was in a town so small, the rats were stoop shouldered.”

Panksepp laughed graciously, but nobody could deliver a one-liner like Youngman. He’d roll the build-up and the punch line into one small, effective package. “What’s the latest dope on Wall Street?” he’d ask. Then, “My son!” Youngman would hit audiences with so many one-liners like this, “machine gun style,” that they wouldn’t quite be able to stop laughing at the last joke before the next one would pile on top. His listeners’ cheeks would ache, and he’d bow a few sour notes on the violin to give them a break. Once before going on stage he was handing off his wife Sadie (on whom he doted) to a theater usher. “Take my wife,” Youngman said distractedly, and when he remembered to say “please” the man in the uniform busted up. A hard working comedian takes his material where he can find it and as it comes, and Youngman repeated that line ten thousand times.

I once met Youngman at the Buffalo Airport. Lake effect squalls had delayed traffic and put the entertainer in a bad mood—he was arguing with his manager. Unable to believe my good luck, I butted in anyway. “Hey Mr. Youngman,” I hollered, “A bum walked up to me, said he hadn’t eaten a square meal in a week.” Youngman swiveled his eyes up and out of the corner of his mouth growled “so I gave him a bouillon cube.” A dozen nearby guffawed at the brush off. As the laughter rippled the old vaudevillian gave me a conspiratorial half-smile—thanks for the set-up, kiddo.

Jokes like Youngman’s take some thinking out. Even short gags call for a process that psychologists term “cortical sophistication,” a human trait arising from the places in the human brain where the powers of language, thought, and memory dwell. When Youngman said, “I was in a town so small that even the rats were stoop-shouldered,” the small-town rats weren’t laughing, and it wasn’t just because the joke was on them. Before we can laugh this way we need to think in sequence: 1. Rats are small, sure, but; 2. even they need to hunch over, when; 3. the blinkered little burg is that confining.

Before we get too smug about a human monopoly on laughter, though, let’s note that chimps can laugh, too. When they’re amused chimps make a kind of breathy, huffing sound. Primatologist Francine Patterson found that when upon teaching gorillas sign-language, they will tell gorilla-jokes. For example, when her keepers refused a thirsty Koko (the famous sign-language trained gorilla) fruit juice, she retrieved a rubber tube, brought it to her face, wagged it about, and then both mimed and signed “sad elephant.”

And here’s where my meeting Panksepp comes in. Thinking a joke through like this isn’t the only way to get a laugh out of a mammal. Laughing is almost original equipment for mammals; it long preceded language. How do we know? Here’s a bigger surprise: we can actually listen to the descendents or our ancient relatives laughing.

At Bowling Green University in the mid 1990’s, professor Panksepp and his enterprising psychology graduate student, Jeff Burgdorf, watched lab rats at play. For fun the scientists also often tickled their subjects as they handled them. Then, needing to bring the rats’ sounds down to human range, they listened in on an ultrasonic bat detector. They learned that rats chirp at various pitches, depending on their activity. They chirp at a particular frequency when they’re tickled, and they chirp at the very same frequency when they wrestle.

Rodent wrestling is simple, the repertoire limited. They mostly go for the nape of the neck and pin the opponent. And they work up a pretty good hip slam, too. Sometimes they stand atop the vanquished, teetering gleefully. Professor Panksepp’s students and colleagues noticed how rats raised in isolation and without play tended to overreact nervously to other rats’ normal movements. Surprises startled them rather than pleased them. Successful play eluded them. Once they became adults, play-deprived rats failed at mating, too. When it comes to rough-and-tumble or slap-and-tickle, they just don’t get the joke. (Panksepp and Burgdorf explain this story more fully in a special issue of the American Journal of Play devoted to neuroscience.)

These plain, enjoyable, endless, ancient rat games teach us humans basic current lessons about the emotional and physical benefits of give-and-take. Rats will become edgy, clumsy, socially isolated, and less creative if deprived of play. Though it’s been 75 million years since we last shared an ancestor, we big-brained, stressed out, modern workaholics can take a cue. Over recent decades, Americans have seen their leisure time shrink; “teaching to the test” has crowded out recess at school; constant texting and tweeting have left us distracted. Old or young, human or rodent, when we get low on play we’re like those dispirited airline travelers waiting for the squall to pass. We’re hungry for a laugh.

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