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What all this means is that pleasure-inducing experiences will be felt in all areas of the brain where dopamine is sent and activated, and all that we sense and the events we recall that surround those experiences will be associated with feeling really good. As an example, Linden points up how associations can make it difficult for hard-core addicts to kick a habit: A cocaine abuser who is used to snorting the drug in a club bathroom might associate the drug with the friends he regularly meets at the club, dance music, a martini, and cigarette smoke. If he’s trying to quit, a trip to the club probably wouldn’t be a good idea, as all those cues might lead to a relapse.

The idea that pleasure is a key mover of behavior is relatively new and has grown along with our understanding of the brain. Prior to the 1950s, scientists thought “punishment avoidance” directed our actions—the application of the stick, never mind the offering of a carrot. Nowadays, entire pharmaceutical companies, new casino cities, fast food chains, and scores of advertising campaigns attempt to shape aspects of our behavior by appealing to our pleasure centers.

Many of the chemicals that trip our dopamine centers carry an odd echo from the world of botany. As plants evolved chemicals to help fight off pests, some evolved to emit substances such as nicotine in tobacco or cannabinoids in marijuana to protect themselves from predation. Bugs stopped buzzing around, and we ended up with the buzz.

Over time, humans have discovered the pleasurable qualities of some plants and fungi to get the dopamine flowing. The ones that jumpstart our pleasure circuits most directly or strongly, including cocaine, nicotine, and opiates, are the most addictive. Method of the drug’s delivery is also important. A Bolivian farmer, Linden notes, can chew on raw leaves of coca and receive some mild stimulation—usually not enough to become a lifelong addict. But a crack smoker who inhales the deeply concentrated burning rock of cocaine gets a knockout punch of pleasure, a punch he wants to take over and over again. Similarly, a cigarette smoker who takes 20 puffs a day from each of 20 cigarettes “gets 400 tiny hits,” Linden points out—hits that reinforce his or her pleasant association with nicotine. Nearly 80 percent of people who try cigarettes become hooked, eclipsing the number who get addicted after giving injected heroin a shot (35 percent), and leaving alcoholics relatively dry (4 percent).

Even though many pleasure circuit triggers are illegal, Linden points out that we’ve been designed to respond to them. The same is the case with so-called behavioral addictions, like gambling or excessive video game playing. Of course, it’s our responsibility to rein in our worst impulses, but we’re not that good at overcoming our attachment to things that light us up. Otherwise, we’d have no addicts, and 12-step program centers would be used for, say, pleasure-igniting meditative yoga. We can put on too much weight from eating too much, but the very act of trying to take it off releases hormones that command us to eat. Dieting, in a real biological sense, is largely a farce.

While genes lay down the brain’s foundation, our wiring is tweaked by how we think and what we do, Linden explains. Our experiences shape the strength and patterns of how our brain fires—a concept that neurophysiologists call plasticity. Studies in twins have shown that genetics is responsible for half of general intelligence levels; nature takes care of the rest. It’s how and what we think that matters.

But some of us are hard-wired for addiction. Given a certain stimulus in the environment, we can become hooked. Let’s revisit those Nauruans. Over the course of many centuries or longer, their ancestors were regularly forced to live through famine and long canoe trips between islands. Like many Micronesian and Polynesian peoples, the Nauru developed a genetic survival mechanism that encouraged their bodies to eat and pack on weight during times of plenty to get through times of little food. When big money and imported fatty, sweet food came from the West, the islanders were genetically ill-equipped to handle it. They packed on pounds continuously, making many of them sick; despite their illnesses, many remained hooked on the food and booze.

For people whose pleasure circuitry has already been commandeered by bad habits, the brain grows in ways that accommodate and encourage the abuse. Memory and association become a curse. “Addiction is nothing more than a memory you can’t shake,” says Linden.

Fortunately, our brains can become turned on by things that don’t hurt us. Generosity, meditation, and prayer can float our boats as well. But just as behavioral addictions tend to have a weaker hold on us than substances, virtues thrum their way through our pleasure centers at yet a lesser rate. Still, Linden says our ability to embrace “good” behaviors with the help of pleasure in the brain is nothing to sneeze at. “When you have these pleasure drives develop along with evolution, and then add in associative learning, a miracle happens. We humans can hijack our reward system arbitrarily, so we can get rewarded by abstract things that have no relationship at all to getting your genes out into the next generation,” he says.

And that might get us to the point where “pleasure” and “happiness” can catch at least a glimpse of each other in the mirror. Because people find meaning in abstract thinking and higher causes, their pleasure centers can start humming when they’re fasting or abstaining from sex. “People push the happiness scale upward when they feel like they’re doing something like making a statement or being artistic or following cultural pursuits—things that are embedded in a social context,” Linden says.

A social context in which we invariably see ourselves at the center. “It really seems clear that we get pleasure from virtuous behaviors we initiate ourselves,” he adds. Playing a concert or taking part in a political rally announces to others—and to our brains—that we’re taking meaningful and pleasurable action. That self-interest can cross over to less-savory events that are hard to predict. “Even something as totally random as gambling, if we throw the dice at the craps table, our pleasure center is very attentive. But if someone else has the dice, not so much. We’re hard-wired to get pleasure from outcomes we have a hand in,” Linden says.

Research into pleasure could lead us toward some solutions to age-old problems. For example, scientists have found that our brains become excited enough by learning to wire themselves in specific and original ways—leading Linden to conclude that educational systems might one day devise better methods for teaching children. “Everyone, including do-gooder parents in Western societies, has decided that children’s learning experiences should be more regimented. But educational systems should spend less time shoving things down kids’ throats and more in letting them take pleasure in self-directed learning,” he says. “If you give most people, particularly kids, the chance to express themselves and be creative, and let them come to it on their own, they’ll surprise you. And they’ll take more pleasure in it than when someone tells them, ‘It’s 11 o’clock. Now’s the time when we draw.’”

Michael Anft is senior writer for Johns Hopkins Magazine.