By Douglas Starr, published on March 1, 2006 - last reviewed on January 21, 2013
They could almost be a couple of kids—chasing, tumbling and squealing with apparent glee. Well, almost like kids. For one thing, their squeals would be impossible to hear without the electronic device that lowers the pitch to the range of human perception. For another, black and white lab rats are not what we think of as fun-loving. Yet here they were, chirping up a storm while engaged in a bout of rough-and-tumble play.
"We studied these sounds for a couple of years without understanding they might be laughter," says Jaak Panksepp, a neuroscientist who maps animal emotions in the brain. Tickling the rats, he has found, provokes the same chirping response observed during rat play. When he momentarily stops the tickling they run to his hand, seeking more. So if you ask whether young rats enjoy playing and tickling, the answer, says Panksepp, is an "unambiguous yes."
It's not an assertion you'd expect to hear from a respected neuroscientist. But Panksepp has made a career out of an even bigger, more heretical argument—that animals have rich emotional lives. Testing rats, dogs, guinea pigs and even chickens from his lab at Bowling Green State University in Ohio since the 1980s, Panksepp has managed to trace animal sadness, fear, rage, maternal attachment and, most surprisingly, a hardwired love of play. Today, working from new digs at Washington State University, he explains that humans don't have a monopoly on emotion; rather, despair, joy and love are ancient, elemental responses that have helped all sorts of creatures survive and thrive in the natural world.
Panksepp's views were once so revolutionary that he was considered a pariah in neuroscience. But over the past several years, a cadre of neuroscientists, psychologists and animal-behaviorists has begun to overturn a centuries-old belief—that unless a creature can talk about its feelings, you can't assume it has them in the first place. Using the modern tools of brain imaging and electrical stimulation, combined with sophisticated field observations, they're finding that mammals display not only the primitive drives of fear and rage, but the softer emotions of love and nurturance, curiosity and play. In short, we've seen a philosophical shift, with the delineation between animal instinct and emotions considered uniquely human breaking down.
When Panksepp started out in the 1970s, his dream was a career in clinical psychology. But his inner scientist quickly took hold. He couldn't treat emotional problems unless he understood their roots, he reckoned, right down to the flux of chemicals that gave rise to feelings in the body and brain. The field was ripe for questions of the sort Panksepp posed. The opiate receptor had just been discovered, and scientists were beginning to understand that at least some of our behavior was a response to chemicals in the brain.
As far as Panksepp was concerned, animal research was the best way to learn more. He started by giving small amounts of opiates to laboratory animals, then observing the impact on primal instincts like hunger, fear and rage. But his true interest veered to the more nuanced, affective emotions—joy, grief, the ecstasy of love—which could dip or soar based on social interactions. He felt animal research was relevant here, as well. Scientists like Jane Goodall were already using words like happiness, sadness, fear and despair to describe chimps they observed in the field. At the same time, the chimp, Washoe, and the gorilla, Koko, were learning human sign language, including vocabulary for words like jealous and love. While some experts dismissed these communications as merely rote, the experiments nonetheless advanced the idea that animals had rich emotional lives.
Yet science demands hard evidence, not just impressions. So over the next thirty years, Panksepp and his graduate students conducted hundreds of experiments to get the kind of cause-and-effect measurements that would conclusively prove the case for animal emotions.
His first target was the separation response—a well-known behavior in which infant mammals desperately struggle and whine when removed from their mothers. In a typical experiment, Panksepp removed five-week-old puppies from their mothers and got the predictable heartrending response. When he gave tiny doses of opiates to the pups, the whining and agitation stopped. His conclusion: Attachment to mother, that most powerful and elemental of emotions, could be turned on or off by chemicals in the brain. Further experiments showed him that the range of social emotions, from the need to interact with others to the force of mother love, could be altered with delivery of neurochemicals, many of them able to comfort, soothe and abrogate loss or pain. Even the need for friends was open to manipulation: A mammal dosed with opiates would be perfectly happy to sit by itself, no matter how social the species.
He knew the chemicals were altering the animals' outward behavior and—seemingly—their inner lives. But where in the brain were those chemical reactions taking place? If Panksepp could trace the reactions to brain structures that animals and humans have in common, it would strengthen his case that not just the behaviors, but the actual emotions, are shared.
First, he tested the assumption, put forth by neuroscientists, that emotion resides in the neocortex, the top level of the brain and the seat of language and thought. To do his experiment, he removed the cortex from baby rats. If his colleagues were right, he could expect the rats to become robotic. Yet the rats grew into emotionally responsive adults, with the full range of play, curiosity and social behavior. (With their learning centers destroyed, of course, they failed at navigating a maze.)
Then, in the grand style of scientists who become research subjects themselves, he flipped the experiment, stimulating his own cortex with a powerful magnetic field. "If the cortex was mediating an emotional response, you'd expect me to feel something," he said. "But I didn't."
Seeking the Center of Joy
If not in the cortex, where does emotion reside? Panksepp spent years using electrical probes to stimulate parts of lab animals' brains and then observing the behaviors provoked. An electrical impulse is a crude stimulation—it carries no information other than a jolt—yet in case after case, he'd stimulate a specific part of a rat's brain and get a coherent emotional response.
Through years of experimentation he found that many emotional circuits converged in a relatively primitive part of the midbrain called the periaqueductal gray, or PAG. Present in all mammals, the PAG produces raw "affects," as he calls them—our basic emotional impulses. It is the PAG that overwhelms us when we grieve, the PAG that signals the brain to bathe us in the soothing hormones of nurturance or the arousing chemicals of love. Panksepp has thus far isolated seven basic emotional drives common to humans and other mammals in sections of the PAG: Predictably, there are fear, rage, lust and separation-distress—all strong, basic drives that most of us would associate with the struggle for survival. But he has also found more subtle emotions, including the quest for nurturance, the desire to offer care and the drive to play.
In humans, these impulses make their way to the brain's higher centers, where they may be processed, modified, inhibited, magnified or even reflected upon. Other mammals lack the ability to reflect on emotion, but they feel it just the same. When you look at your dog bounding on his paws, wagging his tail and playfully panting, you can probably assume he feels happy and eager to interact; when you leave the room and he whimpers, you may conclude he feels sad. What you can't assume, Panksepp says, is that your dog will think back on that happy encounter or sad parting later in the day.
All of which brings us to rat laughter, Panksepp's most controversial work. By tickling the rats, Panksepp and his students elicited laughterlike chirping. When they administered dopamine or electrical stimulation, the effect was the same. The conclusion: The laughter does not arise from learning or conditioning—or from having parents with an urbane sense of humor. It originates as a neurochemical action in the ancient brain structure called the PAG.
Given the origins of laughter and play, says Panksepp, they likely helped us survive and evolve. Other scientists have remarked on the value of play as rehearsal for life's challenges, from hunting to mating. Panksepp has taken it further by proving that play boosts the brain's pleasure-causing dopamine, priming us to respond to changing social situations through neurochemical cues. Play provides a risk-free opportunity to develop adaptive responses to new situations. "This process, which children do on their own, helps create a social brain," Panksepp says.
Panksepp's work suggests an emotional engine for evolution rooted in the ancient brain. Emotions originating in the PAG help animals recognize "comfort zones"—social situations that enhance survival. A pup's chance of survival, for instance, is improved if it's wired to stay near its mother—hence the separation response. Socially skilled pups tend to survive longer, says Panksepp, explaining the rat's love of play.
As Panksepp's colleague Brian Knutson puts it: "The evolutionary goal of a mammal is to survive and procreate. But mammals don't have to be aware of that goal. Your emotional status—things that make you feel good or bad—act as a shorthand."
Few neuroscientists accept so broad a proposition. University of Iowa cognitive neuroscientist and animal behaviorist Mark Blumberg calls Panksepp's assertions about rat laughter, "bordering on irresponsible." Two years ago Blumberg published a paper asserting that rats emit high-frequency chirps in response to changes in temperature and to the physical compression of their chests during rough and tumble play. "Think about laughter in humans," he says. "We don't even know what it is. To assume we know what these emotions are and then project them onto animals is a double error. We just don't have access to the inner lives of animals."
Joseph E. LeDoux, a neuroscientist at New York University who has mapped the neural pathways of the fear response of mammals, says he admires Panksepp's study of behaviors, but hesitates to equate their feelings with emotions played out in the human realm. "I don't deny the existence of animal feelings. I just say it's impossible to know what they feel."
Those who spend time with animals in their natural settings don't have as many doubts. "There are fewer and fewer people who will say carte blanche that dogs don't have feelings," states ethologist Marc Bekoff. It may not be the same as human love, but "of course, dogs show love."
Panksepp's work is still preliminary, and years away from offering cures for human maladies, his original goal. Yet his ideas show practical promise. In looking at the chemistry of social behavior, for example, he finds that rats and dogs given overdoses of opiates lose their need for social connection and retreat to a state much like autism. Panksepp reversed the behavior in rats by treating them with the opiate-blocking chemical naltrexone. Scientists have given naltrexone to autistic humans and found encouraging signs of social alertness.
He's also found connections between drug addiction and social attachment. If morphine can eliminate the distress of separation from a mother, imagine the hold it must have on an addict. The findings may help identify those susceptible to addiction. Understanding the neurochemistry of emotion may also lead to the development of new drugs that target, say, the symptoms of schizophrenia without the emotional "blunting" of today's therapies.
It's a leap to imagine ourselves on an emotional continuum with "lower" animals. Yet we have an amazing amount of DNA in common—upward of 90 percent of our genetic makeup mirrors that of dogs. "It's time," says Panksepp, "for humans to rejoin the rest of the animal kingdom."