Dr. Jaak Panksepp, a neuroscientist at Ohio's Bowling Green State University, has discovered that rats in his lab respond to certain stimuli (tickling and tummy-scratching mainly) by—yes—laughing. Of course, rat laughter isn't your basic, from-the-belly guffaw. "It's more like a chirp," says Panksepp, 55, a native of Estonia and a leading researcher in brain biochemistry.
Panksepp first heard the sound of rat laughter last year when Brian Knutson, 31, a postdoctoral student, recorded the rodents with an instrument that detects high-pitched noises. Played back, the pips, inaudible to the human ear, made the lab sound "like a playground," says Panksepp. "I don't think anyone would say it's chuckling, but it has the same dynamic, repeated feel. It starts to sound pretty happy."
Since mentioning his discovery in April during a presentation, he has been deluged with e-mail and phone calls: "I've had calls from people who have rats as pets who said, 'We knew this was happening!' " So what does all this mean? Panksepp says his findings could help scientists learn which brain systems regulate happiness, perhaps leading to better antidepressants.
The big question, though, remains: Are the rats laughing with the scientists—or at them? Obviously, more research is needed.