If serotonin is the Zen-master among neurotransmitter, dopamine is
Pollyanna,responsible for the highs of infatuation, new love, joy,
self-confidence, and motivation. But like all roller-coaster rides,
dopamine highs have their dangers.
We use the term "falling in love" even though the first giddy days
of a new romance feel buoyant, free from gravity, as if some perfectly
placed wind were boosting us skyward. That sense of becoming airborne is
so unforgettable that years later we may recall it longingly and wonder
why relationships now seem so bound-to-Earth. We may even gaze on our
partners with some dissatisfaction, measuring them against that lost
intensity.
But the gleam of infatuation--if current theory is right--may be
largely the product of unexpectedly potent brain chemistry. And the
primary ingredient in that chemical brew is dopamine, a neurotransmitter
best known for its ability to initiate muscle movement (and thus a key
factor in diseases in which that ability is lost, such as Parkinson's).
These days dopamine's profile is on the rise--the neurotransmitter became
a celebrity in its own right when it graced the cover of Time magazine
last May. But while that story focused on dopamine's role in addiction,
new research suggests that the neurochemical may be similarly important
in triggering the joyously obsessive nature of first love. Rutgers
University anthropologist Helen Fisher, Ph.D., suspects that love's
initial all-consuming sizzle is part pure lust, part pure dopamine. "My
prediction is that dopamine is an essential part of infatuation," says
Fisher, who is now scanning the brains of wildly infatuated people,
probing for that dopamine drive. "Dopamine," she notes, "is already
associated with euphoria, sleeplessness, loss of appetite, and a rush of
motivation." In other words, the dazzling beginnings of love.
But as Fisher's comments suggest, such behaviors have far broader
ramifications. Dopamine now seems everywhere in the brain: running
through four main brain pathways, picked up by five different types of
receptors--each with several subtypes, many still just being defined.
Suddenly, the neurotransmitter is the target of research into happiness,
attention, extroversion, self-confidence, and goal-direction.
"Dopamine, how do I love thee? Let me count the ways," jokes George
Koob, Ph.D., a professor of neuropharmacology at the Scripps Research
Institute in La Jolla, California. Excitement about dopamine is now so
high, says Koob, that the danger is not underestimating its reach but
exaggerating it: "Today's gig is that dopamine is a kind of everyman's
neurotransmitter because it does everything. And the fact is, it
doesn't."
What does it do, then? The long-observed link to Parkinson's
remains dead-on. Starting in the mid-brain and reaching to structures
such as the basal ganglia, dopamine clearly functions as a kind of spark
plug, initiating motor behavior. When the spark fails, the brain's
ability to order appropriate muscle movement fails, too. "You are trapped
in your body," is the way Koob describes it.
In addition, dopamine appears to influence attention and the
ability to concentrate. This is why researchers think that some
dopamine-enhancing drugs, such as Ritalin, help control the jittery,
unfocused behaviors of attention deficit hyperactivity disorder.
Still the most intense excitement among researchers is over the
role of dopamine within the limbic system, a brain region that helps
regulate emotions. Basically, dopamine brightens and highlights our
connections with the world around us, says David Goldman, Ph.D., a
neuro-scientist with the National Institute of Alcohol Abuse and
Alcoholism. "It's essential for associating something that happens with
the feeling of pleasure." In other words, it reinforces behaviors that
make us feel good.
Koob tells an anecdote about B.F. Skinner, Ph.D., the Yale
University psychologist who made famous the whole notion of
reinforcement. According to the story--cheerfully shared among dopamine
researchers--the famed psychologist's class once decided to experiment on
him. So for an entire lecture half the class smiled at him, half glared.
By the end of the session, he was only talking to the beaming side of the
group. "And that, we assume, would have been a dopamine-driven response,"
Koob says.
In this sense, dopamine seems a sort of Pollyanna among
neurotransmitters: It only really responds to the good stuff. In
experiments with monkeys, scientists rewarded some tasks with juice
(apparently beloved by the primates) and punished other tasks with puffs
of air blown in their faces (equally hated.) The monkeys learned to
anticipate either reward or punishment. But the dopamine neurons in their
mid-brain only got active when juice/pleasure was foreseen.
It seems logical to ask, then: If a person is born with a highly
responsive dopamine system, wouldn't he or she be more tuned to receiving
pleasure, to feeling rewarded? Would, in turn, the person with a sluggish
response tend to be unmotivated and less exuberant overall? And what
creates that outlook--the dopamine itself, the receptors that process
dopamine's chemical messages, or some combination of the two? These are
questions researchers are still sorting through.
