Lighten up—according to science, it's good for you

It's a brisk spring afternoon and my son, Charlie, and I are walking to a park with an old friend and her daughter. My son, who just turned 3, grips my hand, focused on getting to the playground as fast as his stubby legs will carry him.

But 5-year-old Gabriela has other ideas. She scrambles up a hill to pluck a fistful of violets and dandelions. She tugs a branch, unleashing a shower of cherry blossoms. Next she's a cat, stalking down the sidewalk on all fours, batting her paws and hissing. "She's been a cat most of the week," my friend explains.

Charlie has had enough. "Stop it, Gabriela," he says. "Stop being a cat! Stop running around! We're supposed to be going to the playground!"

I can't help but think he has a point. The walk, which normally takes 10 minutes, is stretching into a half hour. I've got work to do: papers to grade, stories to research, laundry to fold.

But then I stop and think: What better way than this to spend a spring day? Have I forgotten how to enjoy the journey? Have I forgotten how to have fun?

Ours is an era of seemingly limitless opportunities for fun: costumed bar crawls and bouncy castles, hoverboards and home brewing, blue-and-green mermaid hair, flash mobs, milkshakes adorned with donuts and rock candy.

And yet, everyone seems perpetually stressed, overbooked, and uptight. Even kids seem busy these days, their afternoons packed with practices and lessons. In the words of Zippy the Pinhead, "Are we having fun yet?"

Just what is fun, anyway? What happens in the brain when we have fun? Is there some evolutionary explanation of fun? And what happens if we don't get enough of it? These are tricky questions to pose to a scientist.

Fun is vague. Highly subjective. "It's not a term that scientists use, ever," says David J. Linden, sitting in his ninth-floor office at the School of Medicine. "It's not like I can point to a place in the brain and say, 'Here's what happens when you have fun.'"

But Linden, a neuroscience professor, knows a lot about a concept closely related to fun—pleasure. His book, The Compass of Pleasure (Viking, 2011), explains how experiences as seemingly distinct as drug use, sex, exercise, and altruism have similar effects on the brain. When people—or rats—feel pleasure, neurons activate in a part of the brain called the ventral tegmental area. The long, spindly axons of these neurons reach into other parts of the brain, as the roots of one tree wrap around those of another. When the neuron fires, the ends of the axons release the neurotransmitter dopamine, which is then absorbed by neurons in other regions of the brain.

This pleasure pathway has evolved to reward behavior that benefits survival, both of the individual and the species, says Linda Gorman, teaching professor in the Krieger School's Neuroscience Program. Eating, drinking, and having sex all set these neurons firing. "If it's going to be beneficial to your survival, that reward pathway would be activated," she says.

Mood-altering drugs affect the release and absorption of dopamine, creating a sense of pleasure. They mimic substances that are naturally produced by the body. Morphine and other opium-derived drugs, for example, fit into receptors for the endorphins that the body produces during exercise. A "runner's high," the feeling of euphoria after a long run, is triggered by these endorphins flooding the brain. "This is not uniquely human," says Linden. "Exercise stimulates the pleasure pathways in rats and mice. A rat will press a lever a hundred times to access a running wheel."

The average laboratory mouse will log 5 miles a night on its wheel, and some run as many as 12 miles, he says. Some mice hang on to the wheel after they stop running, whirling around as if on a tiny merry-go-round. Field observations of wild animals suggest the lab rodents are not just trying to break the monotony of being caged. A team of Dutch scientists used food to lure animals to hamster wheels outside. Field mice would eat the treat, then hop on the wheel, running for as long as 18 minutes. Rats, shrews, and even frogs, slugs, and snails, ran—or oozed—along the wheel as well. Even after researchers removed the food, many of these animals returned to the wheel, like miniature fitness buffs.

It's easy to see the evolutionary benefits of exercise triggering the brain's pleasure center. Natural selection would seem to favor animals and humans who get a buzz out of chasing prey or running away from predators. Likewise, it's clear why eating, drinking, and having sex would bring us pleasure. But why do we enjoy activities that are not clearly tied to survival or the propagation of the species? Most people find learning, creating art, exploring new places, and performing charitable acts deeply pleasurable. "What's happened in humans is a miracle," says Linden. "Not only can humans take pleasure from things that have no relation to getting genes to the next generation, but we can take pleasure from things like fasting and celibacy, acts that run counter to the evolutionary imperative."

What's going on here? Perhaps these pleasurable activities could all be seen as a form of play. And play might just be the most important act we can engage in.

We've finally reached the park. Charlie is racing around the playground, blasting imaginary fires with a hose made from a fallen branch. Gabriela has made fast friends with another girl around her age, and they clamber up a spiral pole to cast fairy spells.

We can learn about human play from watching two dogs romping around on a field nearby. They chase each other in circles, roll around, panting and biting. Occasionally, one yelps and the other backs away, the canine equivalent of, "Sorry, my bad." Puppies and young wolves engage in nearly identical play, but, as wolves grow, they play less, while dogs continue to play, says Stuart Brown, the former chief of Psychiatry at Mercy Hospital and Medical Center in San Diego and currently a consulting professor at Stanford's design school, who has spent decades studying animal and human play. As adults, wolves have important business to attend to. They must work out their role in the pack, seek mates, hunt. But humans have bred dogs to remain playful.

The drive to play arises from the most primitive parts of the brain, says Brown, who founded and serves as president of the National Institute for Play, a nonprofit that encourages the study and promotion of play. Studies with rats indicate that the urge to play comes from the limbic system, the part of the brain that controls memory and emotion, Brown says. If researchers remove the cerebral cortex—which controls higher order thought—from rat pups, the pups still learn to play normally with their peers. But though play bubbles up from the more primitive parts of our brains, it helps develop the more complex regions. Juvenile play helps create new pathways in the prefrontal cortex. Rat pups that are barred from play miss out on these connections and are unable to have normal social interactions as adults.

Kids battling with lightsabers or building with LEGO bricks are playing, but what about a girl teaching herself to code? Or a boy training for a hypercompetitive sports team? And how do adults play? Is a round of golf with a client really play? "The state of play is biologically definable as a separate state, as separate as sleep and dreams from our regular consciousness," says Brown. Play is done purely for its own sake, he says. We improvise, experiment, make up new rules to keep the game going. We lose ourselves in play and we lose track of time, which truly does fly when we're having fun. Or, at least, the illusion that time is passing rapidly makes us think that we're having fun, according to an experiment at the University of Chicago devised by researcher Aaron Sackett (he is now at the University of St. Thomas in Minnesota). His team told subjects they had 10 minutes to complete a word task. In reality, they stopped some subjects after five minutes, while others were left with the task for 20 minutes. Those in the five-minute group—for whom time appeared to be flying—rated the task as much more pleasurable.

Freedom and self-direction are also key elements of play. Parents and teachers can make suggestions, but when they dictate the rules, the fun evaporates, says Doris Bergen, an educational psychologist at Miami University in Ohio, who has written many books about play. "The feeling of enjoyment is what's really crucial to play," she says.

How we play changes as we grow. My 6-month-old grabs my husband's nose, catches my eye and laughs, and chews on anything she gets her hands on. Young toddlers mimic their parents by pretending to talk on the phone or rummaging through kitchen cabinets. And older toddlers and school-age children build ever more elaborate games, whether running around in the backyard or immersing themselves in imagined worlds with dolls or dinosaurs or trucks. In the past, most adults were so consumed with survival that play for them was largely confined to festivals and ceremonies.

But as leisure time has increased, so have our opportunities to play, Bergen says. "Almost anything could be play. Some people do math problems for play."

One of the reasons that humans spend more time playing compared to other animals is that our childhoods are so much longer, Linden says. Humans have large brains, but because we walk upright, women have narrow pelvises. In order for babies' heads to be able to pass through the birth canal, they begin life with small brains that take nearly two decades to fully develop.

However, all this play comes at a cost. As Brown points out in his book, Play: How It Shapes the Brain, Opens the Imagination, and Invigorates the Soul (Avery, 2009), play has inherent dangers. Young animals are more likely to die—either by accident or by predator—when they are at play. So the evolutionary benefits must be greater than the risks. What do we gain from play?

First, play provides a safe environment to try out adult behavior. When kittens pounce, bear cubs wrestle, or baby otters swim in circles, they're practicing the skills they will need as adults. Many social animals find their role in the group's hierarchy through play, Brown says. Rats, chimpanzees, and other animals move into dominant or submissive roles based on play. When young animals play, their brains are forging new neural pathways, so that playing in different environments, and surmounting new challenges, allows the brain to become more flexible.

Bergen believes that natural selection has favored playful people because they are more likely to develop strategies to help them adapt to new environments. Early humans who experimented with new techniques for making weapons, picking berries, and crossing streams were honing their survival skills. And play is just as important—or perhaps more so—today as it was for our early ancestors, says Susan Magsamen, senior adviser to the Johns Hopkins Brain Science Institute and Science of Learning Institute. When children play, they're learning how to collaborate, empathize, solve problems, and persevere. Play awakens the sort of thinking that leads us to write novels, compose music, design buildings, and make scientific discoveries. Our exceptional capacity for play sets the stage for all of humanity's great advances.

Magsamen spent her own childhood immersed in creative games with her five sisters, inventing plays and variety shows that they performed for their parents and grandparents. "One sister would make the tickets and one sister would make the sets and then we'd all sing songs from The Partridge Family," she says. That sort of play doesn't stop in adulthood; we just have other names for it. "Creativity and innovation are just big words for play in adults," she says.

If you need cues to know you're having fun, one might be that you're laughing. In antiquity, laughter was feared, says Robert Provine, a neuroscientist and psychology professor at the University of Maryland, Baltimore County. Plato even worried that unrestrained laughter could undermine society, Provine writes in his book, Laughter: A Scientific Investigation (Viking, 2000). Perhaps laughter seems threatening because it is one of the most primitive human sounds. Although everyone laughs a little differently, laughter follows certain set patterns; it has a deep structure. Laughter is instantly recognizable in all human societies. Our closest biological relatives, chimpanzees, laugh in a similar pattern, although their laughter sounds more like panting. "Laughter is a crude part of our primate endowment," Provine says.

Even rats laugh; we just can't hear them. Jaak Panksepp, an affective neuroscientist at Washington State University, was studying rough-and-tumble play in rats when he stuck an audio recorder in their cages. The rats were not wrestling in silence, it turned out, but chirping rhythmically at frequencies we can't detect. But were the rats actually laughing? Panksepp decided to tickle them to find out. It turns out that rats love being tickled, particularly on the backs of their necks. When Panksepp and his assistant stopped tickling them, the rats nuzzled their hands, seeking more. And the rats emitted the same high-frequency chirps, at the same intervals, as they did when they romped with each other. Young rats chirped more than adults. Females chirped more than males. And the rats chirped less when they were tickled in the presence of a stressful stimulus, such as the smell of a cat.

Humans have a complex relationship with laughter, Provine has found. He recorded students engaged in normal conversation and analyzed the remarks that provoked laughter. He found that laughter doesn't always signal fun. Fewer than a fifth of the remarks could be considered humorous. Most were mundane, such as: "How are you?" "Does anyone have a rubber band?" "What is that supposed to mean?"

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Now here's some sobering news about fun: You're probably having less of it now than you did as a child. Pleasure-seeking behavior drops off in young adulthood, says Linden. And our ability to feel some types of pleasure diminishes as we age.

"Our senses degrade as we get older," Linden says. Starting around age 20, we lose 1 percent of our touch receptors each year. That's not particularly noticeable in midlife, but by old age, it leads to problems with balance.

People in the late stages of Parkinson's disease suffer a much more dramatic loss—the brain's pleasure circuitry ceases to function. Patients suffer anhedonia; they no longer enjoy eating, drinking, watching TV, or other activities they once found pleasurable. Drug and alcohol addicts also suffer from anhedonia, even years or decades after they've stopped using, Linden says. Excessive drug use can fry the brain's pleasure circuitry. People with a genetic predisposition to addiction already derive less pleasure from using intoxicants than others, Linden says. "The genetic variants that make you pleasure-seeking also make you less likely to enjoy pleasure."

Since stress triggers addictive behavior, people should take part in activities that reduce it—exercise, meditation or prayer, and play, Linden says. "The answer is to take your pleasure widely. Mix your virtues and your vices."

Play experts caution that the highly scheduled days of today's children allow less time for true play. "If there's an adult in charge, and you have to do it a certain way or you'll be critiqued—that is absolutely not play," says Bergen. "That is work disguised as play." Brown, of the National Institute for Play, says we're suffering from a national "play deficit." Cuts to recess time in school and ever-increasing academic expectations encroach on play time. And a culture that prizes busyness means that adults have less time to goof off. "It's a public health problem," Brown says. Depression, anxiety, and irritability are all symptoms of a lack of play, he says.

So perhaps we adults should make more time for play, whether that means planting a garden, joining a bocce league, dancing, or rediscovering a childhood pastime. "We almost have a guilt about it," says Magsamen. "If we're playing, we must not be working. But if you're not playing, everything else doesn't go as well. Giving yourself permission to enjoy things makes all of your life fuller and richer."

The kids skateboarding down the street, sipping imaginary tea, and building a pillow fort are learning just as much—perhaps more—as a peer in a piano lesson. Since our walk to the park with Gabriela, I've been trying to weave more fun into my days with my kids. The more we dawdle on our strolls, the more we discover: ant colonies in the sidewalk, frogs by the stream, and a pile of rocks that makes the perfect bear cave. We helicopter maple seeds, toss petals in the air, and cook bowls of mulch at the playground. Sometimes we even pretend we're cats.