多巴胺是：爱欲？赌博？奖赏？成瘾？
2015-08-11 22:48阅读：
多巴胺是：爱欲？赌博？奖赏？成瘾？
http://www.slate.com/articles/health_and_science/science/2013/07/what_is_dopamine_love_lust_sex_addiction_gambling_motivation_reward.html
Dopamine Is _________
Is it love? Gambling? Reward? Addiction?
By Bethany Brookshire
Colored MRI Scan Of Human Brain.
An MRI scan of the human brain
Photo by Katie Nesling/Thinkstock
In a brain
that people love to describe as “awash with chemicals,” one
chemical always seems to stand out. Dopamine: the molecule behind
all our most sinful behaviors and secret cravings. Dopamine is
love. Dopamine is lust. Dopamine is adultery. Dopamine is
motivation. Dopamine is attention. Dopamine is feminism. Dopamine
is addiction.
My, dopamine’s been busy.
Dopamine is the one neurotransmitter that everyone seems to
know about. Vaughn Bell once called it the Kim Kardashian of
molecules, but I don’t think that’s fair to dopamine. Suffice it to
say, dopamine’s big. And every week or so, you’ll see a new article
come out all about dopamine.
So is dopamine your cupcake addiction? Your gambling? Your
alcoholism? Your sex life? The reality is dopamine has something to
do with all of these. But it is none of them. Dopamine is a
chemical in your body. That’s all. But that doesn’t make it
simple.
What is dopamine? Dopamine is one of the chemical signals
that pass information from one neuron to the next in the tiny
spaces between them. When it is released from the first neuron, it
floats into the space (the synapse) between the two neurons, and it
bumps against receptors for it on the other side that then send a
signal down the receiving neuron. That sounds very simple, but when
you scale it up from a single pair of neurons to the vast networks
in your brain, it quickly becomes complex. The effects of dopamine
release depend on where it’s coming from, where the receiving
neurons are going and what type of neurons they are, what receptors
are binding the dopamine (there are five known types), and what
role both the releasing and receiving neurons are
playing.
And dopamine is busy! It’s involved in many different
important pathways. But when most people talk about dopamine,
particularly when they talk about motivation, addiction, attention,
or lust, they are talking about the dopamine pathway known as the
mesolimbic pathway, which starts with cells in the ventral
tegmental area, buried deep in the middle of the brain, which send
their projections out to places like the nucleus accumbens and the
cortex. Increases in dopamine release in the nucleus accumbens
occur in response to sex, drugs, and rock and roll. And dopamine
signaling in this area is changed during the course of drug
addiction. All abused drugs, from alcohol to cocaine to
heroin, increase dopamine in this area in one way or another, and
many people like to describe a spike in dopamine as “motivation” or
“pleasure.” But that’s not quite it. Really, dopamine is signaling
feedback for predicted rewards. If you, say, have learned to
associate a cue (like a crack pipe) with a hit of crack, you will
start getting increases in dopamine in the nucleus accumbens in
response to the sight of the pipe, as your brain predicts the
reward. But if you then don’t get your hit, well, then dopamine can
decrease, and that’s not a good feeling. So you’d think that maybe
dopamine predicts reward. But again, it gets more complex. For
example, dopamine can increase in the nucleus accumbens in people
with post-traumatic stress disorder when they are experiencing
heightened vigilance and paranoia. So you might say, in this brain
area at least, dopamine isn’t addiction or reward or fear. Instead,
it’s what we call salience. Salience is more than attention: It’s a
sign of something that needs to be paid attention to, something
that stands out. This may be part of the mesolimbic role in
attention deficit hyperactivity disorder and also a part of its
role in addiction.
But dopamine itself? It’s not salience. It has far more roles
in the brain to play. For example, dopamine plays a big role in
starting movement, and the destruction of dopamine neurons in an
area of the brain called the substantia nigra is what produces the
symptoms of Parkinson’s disease. Dopamine also plays an important
role as a hormone, inhibiting prolactin to stop the release of
breast milk. Back in the mesolimbic pathway, dopamine can play a
role in psychosis, and many antipsychotics for treatment of
schizophrenia target dopamine. Dopamine is involved in the frontal
cortex in executive functions like attention. In the rest of the
body, dopamine is involved in nausea, in kidney function, and in
heart function.
With all of these wonderful, interesting things that dopamine
does, it gets my goat to see dopamine simplified to things like
“attention” or “addiction.” After all, it’s so easy to say
“dopamine is X” and call it a day. It’s comforting. You feel like
you know the truth at some fundamental biological level, and that’s
that. And there are always enough studies out there showing the
role of dopamine in X to leave you convinced. But simplifying
dopamine, or any chemical in the brain, down to a single action or
result gives people a false picture of what it is and what it does.
If you think that dopamine is motivation, then more must be better,
right? Not necessarily! Because if dopamine is also “pleasure” or
“high,” then too much is far too much of a good thing. If you think
of dopamine as only being about pleasure or only being about
attention, you’ll end up with a false idea of some of the problems
involving dopamine, like drug addiction or attention deficit
hyperactivity disorder, and you’ll end up with false ideas of how
to fix them.
The other reason I don’t like the “dopamine is” craze is
because the simplification takes away the wonder of dopamine. If
you believe “dopamine is,” then you’d think that we’ve got it all
figured out. You begin to wonder why we haven’t solved this
addiction problem yet. Complexity means that the diseases
associated with dopamine (or with any other chemical or part of the
brain, for that matter) are often difficult to understand and even
more difficult to treat.
By emphasizing dopamine’s complexity, it might feel like I’m
taking away some of the glamour, the sexiness, of dopamine. But I
don’t think so. The complexity of how a neurotransmitter behaves is
what makes it wonderful. The simplicity of a single molecule and
its receptors is what makes dopamine so flexible and what allows
the resulting systems to be so complex. And it’s not just dopamine.
While dopamine has just five receptor type, another
neurotransmitter, serotonin, has 14 currently known and even more
that are thought to exist. Other neurotransmitters have receptors
with different subtypes, all expressed in different places, and
where each combination can produce a different result. There are
many types of neurons, and they make billions and billions of
connections. And all of this so you can walk, talk, eat, fall in
love, get married, get divorced, get addicted to cocaine, and come
out on top of your addiction some day. When you think of the sheer
number of connections required simply for you to read and
understand this sentence—from eyes to brain, to processing, to
understanding, to movement as your fingers scroll down the page—you
begin to feel a sense of awe. Our brain does all this, even while
it makes us think about pepperoni pizza and what that text your
crush sent really means. Complexity makes the brain the fascinating
and mind-boggling thing that it is.
So dopamine has to do with addiction, whether to cupcakes or
cocaine. It has to do with lust and love. It has to do with milk.
It has to do with movement, motivation, attention, psychosis.
Dopamine plays a role in all of these. But it is none of them, and
we shouldn’t want it to be. Its complexity is what makes it great.
It shows us what, with a single molecule, the brain can
do.
Bethany Brookshire recently completed a postdoc in behavioral
neuroscience at the University of Pennsylvania School of Medicine.
She blogs for Scientific American at The Scicurious Brain and for
Scientopia at Neurotic Physiology. You can follow her on Twitter at
@scicurious.
【博文链接】为全球该领域最新的顶级研究，最终指向肥胖其实是“食物成瘾”，“食瘾”与“烟瘾、赌瘾、爱瘾”等生理机制完全一样，这是解决肥胖问题的终极钥匙
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