By Kathleen Yount

A lot of what we know about the physiology of happiness came from some rather unhappy business indeed. Recall the plight of poor Phineas Gage. Phineas was a good man by any century’s standards, diligent and popular with everyone he worked with on the railroads of Vermont. But in the fall of 1848, while laying dynamite along the tracks, Gage accidentally struck and detonated an exposed pack with his tamping iron. The metal rod quite literally flew through his head—in through his left cheek, behind his eye, and out through the back of his skull.

Miraculously, Gage was walking and talking again shortly after the accident. But it quickly became clear that he wasn’t the man he used to be. “He is . . . irreverent, indulging at times in the grossest profanity,” said his employer, who refused to rehire him because this once-happy and well-liked man suddenly was “manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires . . . obstinate, yet capricious and vacillating. . . . his mind was radically changed, so that his friends and acquaintances said he was no longer Gage.”

Today’s technology has allowed researchers to carefully reconstruct the preserved remains of Gage’s skull and determine that the part of his brain that was obliterated by the tamping iron was the prefrontal cortex. Therein lies one anatomical component of happiness in the brain. But “happiness” is not a word scientists use often in their work. UAB neurobiologist Robin Lester, Ph.D., says that researchers are more likely to use the term “positive affect” to discuss the neurobiology of positive emotions. “Happiness is lumped into that concept,” he says, “because it allows you to discuss things like safety from danger. For an animal, at least, happiness is being safe from danger.” Lester says that being in what’s called a highly motivated state is also positive affect. “People who are risk-takers or highly motivated tend to be happier in general.”

Neurobiologists are using modern tools such as functional imaging to study how brain injuries—as well as powerful negative emotions such as fear—stimulate different parts of the brain. In this way they have slowly mapped out much of the brain’s geography of happiness. What they’ve learned from these studies is that happiness doesn’t seem to have a clearly defined neurobiological home. Like everything else about human nature, happiness has complex roots.

Your Happiness Housekeepers

When you hear a funny joke, your laughter response is generated in the prefrontal cortex of your brain. People who have undergone prefrontal lobotomies experience drastic alterations of their personalities, as did Phineas Gage. But this is one of the more conscious coordinates of happiness in the head. At its fundamental level, says Lester, happiness—like all other emotional states—is under the brain’s subconscious control. “That’s because emotional states are important for regulating behaviors in general,” he explains. Anyone who’s been sleepless with worry or too heartsick to eat knows that a certain amount of positive affect is necessary to make sure you properly eat, drink, sleep, have sex, and do all the other things humans need to do to survive, thrive, and propagate our species. The brain uses—and depends on—our emotions to make sure of it.

One crucial part of that process is the hypothalamus, a tiny, subcortical structure shaped not unlike a very melty ice-cream cone. Its bottom tip rests on the chickpea-sized pituitary gland, which it uses to link the nervous system with the endocrine system. The main job of the hypothalamus is to maintain what neurobiologists call the “set point”—a unique and fixed status quo in each person’s body. It registers stimuli from inside the body, such as your glucose level, and outside the body, such as whether or not you’re currently being chased by a bear. Everything from blood pressure to body weight falls under the purview of the hypothalamus; it controls hunger, thirst, sexual drive, and circadian rhythms. “The hypothalamus integrates internal and external information,” says Lester, “so that it can send out appropriate signals to control your response to a specific situation.”

The hypothalamus is part of the limbic system of the brain—an old system, says Lester, responsible for emotional processing and learning. A variety of brain structures play a role in this system, including the amygdala, or “fear center,” and the nucleus accumbens, or “pleasure center.” “There is some conscious control of the limbic system,” he says, “but it can do a lot of stuff automatically.” Take smiling, for example—a universal expression of happiness that crosses all cultures. “In patients undergoing brain surgery,” says Lester, “researchers have shown that by stimulating the nucleus accumbens, you can induce a patient to smile. In fact, you can also induce feelings of mirth, so the person will actually feel happy.” The activities of these basic, often subconscious processes ultimately register in the personality center of the prefrontal cortex as emotions.

Currents of Joy

But it’s not just the physical structures along the happiness pathway that are important. It’s also what travels between them—the chemical foot patrol that turns up one response and dampens down another. These chemical signals, called neurotransmitters—including serotonin, dopamine, and norepinephrine—are required at certain levels in the brain to maintain your happiness status quo. Too little of them can result in clinical depression—inappropriate unhappiness, one could say. Other signals, such as endorphins and enkephalins, the body’s natural analgesics, contribute to positive affect through the mood elevation we get after exercise. Together, these signals create a current that runs from our most primordial brain structures to our highest cerebral echelons, and its ebb and flow seems to have a profound effect on our emotional highs and lows.

In addition to the pleasure center, the fear center, and the homeostasis mechanisms in the brain, Lester notes that the brain’s “reward system,” a concentration of neurons that transmit dopamine, is an important trail on the happiness map. “The reward system is essential for driving motivated behaviors that are responsible for the survival of self and species,” he says. “These are really fundamental behaviors, so this is a very powerful system. And you’ll find that in people who are extroverted, or risk-takers, this system is kind of tuned up. They have a more active dopaminergic system.”

Unhappiness Has Its Uses

Dopamine and its fellow neurotransmitters also provide an excellent illustration of why happiness, homeostatically speaking, is a thing best meted out judiciously. “That’s to say,” says Lester, “that from a biologist’s point of view, it’s not necessarily a good thing to be happy all the time.” This is because happy brains don’t necessarily function in the most practical ways for long-term well-being. In fact, “we tend to really make a mess of making the right predictions about what will give us happiness in the longterm,” he says.

“The classic example is shopping for a new television. You get excited about the TV with the best picture. So you don’t take into account whether it will integrate with your other entertainment devices, whether it’s out of the price range you can afford, and other things. So if you buy the TV that makes you happiest in the store, you end up not being happy.” The same model could be applied to other areas of life, from choosing a career to choosing a mate.

“Happiness is only one emotion we need to make sure we do the right things,” says Lester. “If you’re confronted by a tiger, it’s not a good time to react by feeling happy.” While that example is extreme, the concept holds true for more mundane experiences. In fact, studies suggest that unhappiness or mild depression might serve a social purpose. “Let’s say you’re moving through positions of increasing responsibility at work,” says Lester. “You might get to a point where it’s too much. That level is different for each person, so depression—lowering your level of happiness—might be your brain’s way of indicating that you’re not at the level that’s best for you.”

Slaves to Biology?

Useful or not, it goes without saying that unhappiness is unpleasant, and there are times when our conscious minds want to chase those blues away. Luckily, says Lester, our emotions are not complete captives to the brain’s structures and signaling mechanisms. “Happiness depends on information that is constantly cycling throughout cortical and subcortical, conscious and subconscious brain systems,” he says. “Psychologists will tell you that through cognitive behavioral therapies you can reset some of this yourself.”

If the level of a transmitter affects your state of mind, it stands to reason that you can use your mind to affect the level of the transmitter. A very basic example is hunger: “The hypothalamus samples things like your glucose level, and that helps tell you whether you’re hungry or not,” says Lester. “You’re not going to be happy if you’re very hungry—but then you might consciously engage the reward pathway by saying, ‘Well, I’m looking forward to getting something to eat later on,’ which will elevate your mood.”

Lester notes that it can be hard to separate the psychologic from the physiologic components that drive happiness. “But we do know from behavioral therapies that if you change your behaviors, you can change your brain chemistry—that is, within limits.

“These processes, though they can operate below conscious level, are not entirely subconscious. That probably gives us an advantage over lower species, because we have more cortical control over our reward pathway. An animal is probably critically dependent on its brain’s reward system to generate the appropriate response for a given situation. But we get more of a chance to think about it.” Lester pauses a moment, and smiles. “Maybe that’s good, and maybe it’s not.”

Seeking the Aerial View

Though neurobiologists know many of the locations on the brain’s happiness map, they are still working to develop a comprehensive understanding of the human emotional landscape. “We’re talking about only a few small groups of neurons that contain the transmitters, but they transmit throughout the brain,” Lester says. “The big question we’re left with is how all these systems integrate to control emotional behavior. There’s a lot we can still learn about that.”

Lester says the genetic basis of happiness is an especially rich area for ongoing study. “It’s pretty intriguing, the question of why some people say they’re happier than others. We’re all very different in that respect. And it has to be some combination of our experience and our genetics.” With advances in genetic understanding and human imaging, Lester believes a clearer sense of the physiology that influences emotion will form. “As these technologies improve, we’ll better understand this happiness thing.”