But there is a growing consensus that the dopamine network does influence everyday behaviors. There is even speculation that by pursuing certain behaviors--single-mindedly focusing on a project, for instance--a person might increase that dopamine drive. Richard Depue, Ph.D., professor of human development at Cornell University, points out that goal-directed behavior (or the lack of it) tends to stand out as a major personality trait. Put simply, some of us are motivated to pursue goals and others are not. Depue believes it's the dopamine system that explains that difference. "When our dopamine system is active, we are more positive, excited, and eager to go after goals and rewards, whether it's food, sex, money, education, or professional achievement," he says. In fact, he suggests that people who are goal-directed are not only more motivated but are generally happier. "We have strong evidence that feelings of elation [that occur] because you are moving toward achieving an important goal are biochemically based, though they can be modified by experience."
If we compare dopamine to serotonin--another "happiness" neurotransmitter--it becomes clear that dopamine requires a cautious approach. Serotonin is a Zen master among neurotransmitters, linked to tranquillity, reason, calm. The best-selling antidepressants on the market--the Prozac family--keep serotonin levels high by preventing neurons from reabsorbing the neurotransmitter after it has been released, thus increasing its availability. Prozac users talk of an emotional leveling, a gradual disappearance of the depressive free-fall. "Prozac is not an abusable drug and never will be," Koob says. "There's no tangible effect the first time you take it. It just slowly helps regulate the system."
There's nothing Zen about dopamine; it doesn't call up thoughts of monasteries and meditation, but of more breathless images--a teenager standing up in a plummeting roller-coaster car, perhaps. There's a body of work, still debated by researchers, that links dopamine directly to novelty-seeking and risk-taking behaviors.
It's not surprising, then, that dopamine is suspected of facilitating the effects of not just Ritalin but more troubling drugs as well. As alcohol concentrations build in the body, the brain responds by releasing more dopamine. Cocaine also seems to stimulate a dopamine rush. And with that comes a high-flying sense of pleasure, power, concentration, a jazzed-up sense of energy. It's well known that rats and other lab animals will perform tasks devotedly and sometimes desperately in return for a cocaine hit once they become addicted. That behavior continues unless scientists block their dopamine transport system. Then the drug suddenly falls into the ho-hum category. Without dopamine, cocaine would apparently be nothing more than white, powdery stuff with a funny taste.
Richard Mailman, Ph.D., a professor of psychiatry and pharmacology at the University of North Carolina at Chapel Hill, points out that a pleasure-reward system in the brain is, in an evolutionary sense, a terrific idea. It pushes us toward accomplishment, achievement, improving ourselves. "But it's supposed to be a subtle system," he says. "With cocaine, you get a jackhammer effect." There are hints, in fact, that the body tries to keep dopamine in check. And there's growing evidence that too much dopamine--notably in the limbic system--plays a role in the development of schizophrenia. A number of antipsychotic medications seem to suppress goal-oriented behaviors and interest in the world, a strong suggestion that the drugs are suppressing dopamine's effects.
Mailman emphasizes that dopamine does not work in isolation; indeed, many scientists suspect that dopamine and serotonin may interact--in some complicated and poorly understood ways--to produce psychotic illnesses such as schizophrenia. But researchers are currently fascinated by the dopamine angle, with its hints of how thin the line may be between intensity and insanity. One of the newest theories holds that dopamine initiates not only thoughts of pleasure, but perhaps initiates thought itself. "The idea is that schizophrenia is a result of dopamine hyper-activity," Koob explains. "The person is bombarded with so many thoughts their ability to pay attention to what's real and what's not is overwhelmed."
Given all this, perhaps it's reassuring that Fisher suspects that the dopamine high of first love is meant to be a merely transient pleasure. "When I first started looking at the properties of infatuation, they had some of the same elements of a cocaine high: sleeplessness, loss of a sense of time, absolute focus on love to the detriment of all around you. People walk out of marriages, abandon children. Infatuation can overtake the rational parts of your brain."
Fisher theorizes that different neurochemicals influence different stages of male-female relationships, which she categorizes as lust (driven mainly by hormones), attraction/infatuation (dopamine), and attachment. As we move into attachment--long-standing relationships--it may be that serotonin or hormones, such as oxytocin, that are associated with nurturing behaviors become more important. For partners and parents, such stability is essential. It is those who never grow out of infatuation, who remain obsessed with love, that may eventually become dangerous lovers--stalkers, for instance.
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