In a 2003 study Panksepp and Bowling Green State University neurobiologist Jeff Burgdorf demonstrated that if rats are tickled in a playful way, they readily chirp. Rats that were tickled bonded with the researchers and became rapidly conditioned to seek tickles.
Understanding the chirping of the rats may help scientists better understand human laughter.
"Deciphering the neutral circuitry of playful chirping in rats is an important goal of future research," Panksepp writes in his Science article. "Such knowledge may help to reveal how joking and horsing around emerged in our expansive higher brain regions."
From Pant-Pant to Ha-Ha
Robert Provine, a psychology professor at the University of Maryland in Baltimore, agrees there is an evolutionary continuity of laughter. Its origin is in tickling and rough-and-tumble play, he says.
Provine, the author of Laughter: A Scientific Investigation, and other scientists have studied chimpanzees and found a link between their laughter-like noises and human laughter.
"Laughter is literally the sound of play, with the primal 'pant-pant'the labored breathing of physical playbecoming the human 'ha-ha,'" Provine said.
By studying the transition between the panting of chimps and the human ha-ha, scientists discovered that breath control is the key to the emergence of both human laughter and speech.
The sources of play and laughter in the brain are instinctual, many scientists believe. If so, the many instinctive behaviors of other animals could help researchers better understand consciousness and other human conditions.
"For example, we may be conscious less than we think and overestimate consciousness and its influence on our lives," Provine said. "We are not, for example, conscious of unconsciousness. Regarding laughter, since it's not consciously controlledtry to laugh on command!we don't speak laughter the way we choose words in speech."
Scientists also hope to track down the genes that control joy.
"Perhaps we will even stumble on new molecules to alleviate depression as well as disorders of excessive exuberance [such as mania and attention deficit/hyperactivity disorder]," Panksepp writes in Science.
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