Friday, April 01, 2005
Animals enjoy good laugh too, scientists say
Tickling rats to make them chirp with joy may seem frivolous as a scientific pursuit, yet understanding laughter in animals may lead to revolutionary treatments for emotional illness, researchers suggest.
Joy and laughter, they say, are proving not to be uniquely human traits.
Roughhousing chimpanzees emit characteristic pants of excitement, their version of "ha-ha-ha" limited only by their anatomy and lack of breath control, researchers contend.
Dogs have their own sound to spur other dogs to play, and recordings of the sound can dramatically reduce stress levels in shelters and kennels, according to the scientist who discovered it.
Even laboratory rats have been shown to chirp delightedly above the range of human hearing when wrestling with each other or being tickled by a keeper--the same vocalizations they make before receiving morphine or having sex.
Studying sounds of joy may help us understand the evolution of human emotions and the brain chemistry underlying such emotional problems as autism and attention-deficit/hyperactivity disorders, said Jaak Panksepp, a pioneering neuroscientist who discovered rat laughter.
Panksepp, of Bowling Green State University in Ohio, sums up the latest studies in this week's edition of the journal Science in hopes of alerting colleagues to results that he terms "spectacular." The research suggests that studying animal emotions, once a scientific taboo, seems to be moving rapidly into the mainstream.
"It's very, very difficult to find skeptics these days. The study of animal emotions has really matured.
Things have changed completely from as recently as five years ago," said Mark Bekoff, an expert in canine play behavior and professor of biology at the University of Colorado, Boulder.
Biologists suggest that nature apparently considers sounds of joy important enough to have conserved them during the evolutionary process.
"Neural circuits for laughter exist in very ancient regions of the brain," Panksepp said, "and ancestral forms of play and laughter existed in other animals eons before we humans came along."
Research in this area "is just the beginning wave of the future," said comparative ethologist Gordon Burghardt, of the University of Tennessee, who studies the evolution of play. "It will allow us to bridge the gap with other species."
New investigative techniques often rely on super high-tech scanning wizardry, but the most important tool for scientists in this field is much more simple.
"Tickles are the key," Panksepp said. "They open up a previously hidden world."
Panksepp had studied play vocalizations in animals for years before it occurred to him that they might be an ancestral form of laughter.
"Then I went to the lab and tickled some rats. Tickled them gently around the nape of their necks. Wow!"
The tickling made the rats chirp happily--"as long as the animal's friendly toward you," he said. "If not, you won't get a single chirp, just like a child that might be suspicious of an adult."
Rats that were repeatedly tickled became socially bonded to the researchers and would seek out tickles. The researchers also found that rats would rather spend time with animals that chirp a lot than with those that don't.
During human laughter, the dopamine reward circuits in the brain light up. When researchers neurochemically tickled those same areas in rat brains, the rats chirped.
Rat humor remains to be investigated, but if it exists, a prime component will be slapstick, Panksepp speculated. "Young rats, in particular, have a marvelous sense of fun."
Panksepp said that laughter, at least in response to a direct physical stimulus such as tickling, may be a common trait shared by all mammals.
Psychologist and neuroscientist Robert Provine, author of "Laughter: A Scientific Investigation," tickled and played with chimpanzees at the Yerkes Regional Primate Center in Atlanta while researching the origins of the human laugh.
Laughter in chimps, our closest genetic relatives, is associated with rough-and-tumble play and tickling, Provine found. That came as no surprise.
"It's like the behavior of young children," said Provine, of the University of Maryland Baltimore County. "A tickle and laughter are the first means of communication between a mother and her baby, so laughter appears by about four months after birth."
The importance of such an early behavior is apparent.
"We're talking about a life-and-death deal here--the bonding and survival of babies," Provine said.
When chimps laugh, they make unique panting sounds, ranging from barely audible to hard grunting, with each inward and outward breath.
"We humans laugh on outward breaths. When we say `ha-ha-ha,' we're chopping an outward breath," Provine said. "Chimps can't do that. They make one sound per inward and outward breath. They don't have the breath control to ... make the traditional human laugh."
The breakthrough in dog laughter was accomplished by University of Nevada, Reno, researcher Patricia Simonet while working with undergraduates at Sierra Nevada College in Lake Tahoe.
With extensive chimp research behind her, Simonet was open to the idea of animal emotions, but the laughing sound she discovered in dogs was unexpected: a "breathy, pronounced, forced exhalation" that sounds to the untrained ear like a normal dog pant.
But a spectrograph showed a burst of frequencies, some beyond human hearing. A plain pant is simpler, limited to just a few frequencies.
Hearing a tape of the dog laugh made single animals take up toys and play by themselves, Simonet said. It never initiated aggressive responses.
"If you want to invite your dog to play using the dog laugh, say `hee, hee, hee' without pronouncing the `ee,'" Simonet said. "Force out the air in a burst, as if you're receiving the Heimlich maneuver."
When she played a recording of a laughing dog at an animal shelter, Simonet found that even 8-week-old puppies reacted by starting to play, something they hadn't done when exposed to other dog sounds.
"Some sounds, like growls, confused the puppies. But the dog laugh caused sheer joy and brought down the stress levels in the shelter immediately."
Posted by C. at 10:44 AM