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Hijacking the Brain Circuits With a Nickel Slot Machine
By SANDRA BLAKESLEE
Compulsive gambling, attendance at sporting events, vulnerability to
telephone scams and exuberant investing in the stock market may not seem
to have much in common. But neuroscientists have uncovered a common
Such behaviors, they say, rely on brain circuits that evolved to help
animals assess rewards important to their survival, like food and sex.
Researchers have found that those same circuits are used by the human
brain to assess social rewards as diverse as investment income and
surprise home runs at the bottom of the ninth.
And, in a finding that astonishes many people, they found that the brain
systems that detect and evaluate such rewards generally operate outside
of conscious awareness. In navigating the world and deciding what is
rewarding, humans are closer to zombies than sentient beings much of the
The findings, which are gaining wide adherence among neuroscientists,
challenge the notion that people always make conscious choices about
what they want and how to obtain it. In fact, the neuroscientists say,
much of what happens in the brain goes on outside of conscious awareness.
The idea has been around since Freud, said Dr. Gregory Berns, a
psychiatrist at Emory University School of Medicine in Atlanta.
Psychologists have studied unconscious processing of information in
terms of subliminal effects, memory and learning, he said, and they have
started to map out what parts of the brain are involved in such
processing. But only now are they learning how these different circuits
interact, he said.
"My hunch is that most decisions are made subconsciously with many
gradations of awareness," Dr. Berns said. "For example, I'm vaguely
aware of how I got to work this morning. But consciousness seems
reserved for more important things."
Dr. P. Read Montague, a neuroscientist at Baylor College of Medicine in
Houston, says the idea that people can get themselves to work on
automatic pilot raises two questions: how does the brain know what it
must pay conscious attention to? And how did evolution create a brain
that could make such distinctions?
The answer emerging from experiments on animals and people is that the
brain has evolved to shape itself, starting in infancy, according to
what it encounters in the external world.
As Dr. Montague explained it, much of the world is predictable:
buildings usually stay in one place, gravity makes objects fall, light
falling at an oblique angle makes long shadows and so forth. As children
grow, their brains build internal models of everything they encounter,
gradually learning to identify objects and to predict how they move
through space and time.
As new information flows into it from the outside world, the brain
automatically compares it to what it already knows. If things match up —
as when people drive to work every day along the same route — events,
objects and the passage of time may not reach conscious awareness.
But if there is a surprise — a car suddenly runs a red light — the
mismatch between what is expected and what is happening instantly shifts
the brain into a new state. A brain circuit involved in decision making
is activated, again out of conscious awareness. Drawing on past
experience held in memory banks, a decision is made: hit the brake,
swerve the wheel or keep going. Only a second or so later, after hands
and feet have initiated the chosen action, does the sense of having made
a conscious decision arise.
Dr. Montague estimates that 90 percent of what people do every day is
carried out by this kind of automatic, unconscious system that evolved
to help creatures survive.
Animals use these circuits to know what to attend to, what to ignore and
what is worth learning about. People use them for the same purposes
which, as a result of their bigger brains and culture, include listening
to music, eating chocolate, assessing beauty, gambling, investing in
stocks and experimenting with drugs — all topics that have been studied
this past year with brain imaging machines that directly measure the
activity of human brain circuits.
The two circuits that have been studied most extensively involve how
animals and people assess rewards. Both involve a chemical called
dopamine. The first circuit, which is in a middle region of the brain,
helps animals and people instantly assess rewards or lack of rewards.
The circuit was described in greater detail several years ago by Dr.
Wolfram Schultz, a neuroscientist at Cambridge University in England,
who tracked dopamine production in a monkey's midbrain and experimented
with various types of rewards, usually squirts of apple juice that the
Dr. Schultz found that when the monkey got more juice than it expected,
dopamine neurons fired vigorously. When the monkey got an amount of
juice that it expected to get, based on previous squirts, dopamine
neurons did nothing. And when the monkey expected to get juice but got
none, the dopamine neurons decreased their firing rate, as if to signal
a lack of reward.
Scientists believe that this midbrain dopamine system is constantly
making predictions about what to expect in terms of rewards. Learning
takes place only when something unexpected happens and dopamine firing
rates increase or decrease. When nothing unexpected happens, as when the
same amount of delicious apple juice keeps coming, the dopamine system
In animals, Dr. Montague said, these midbrain dopamine signals are sent
directly to brain areas that initiate movements and behavior. These
brain areas figure out how to get more apple juice or sit back and do
nothing. In humans, though, the dopamine signal is also sent to a higher
brain region called the frontal cortex for more elaborate processing.
Dr. Jonathan Cohen, a neuroscientist at Princeton, studies a part of the
frontal cortex called the anterior cingulate, located in back of the
forehead. This part of the brain has several functions, Dr. Cohen said,
including the task of detecting errors and conflict in the flow of
information being processed automatically.
Brain imaging experiments are beginning to show that when a person gets
an unexpected reward — the equivalent of a huge shot of delicious apple
juice — more dopamine reaches the anterior cingulate. When a person
expects a reward and does not get it, less dopamine reaches the region.
And when a person expects a reward and gets it, the anterior cingulate
When people expect a reward and do not receive it, their brains need a
way to register the fact that something is amiss so it can recalibrate
expectations for future events, Dr. Cohen said. As in monkeys, human
dopamine neurons project to areas that plan and control movements, he
said. Fluctuating levels of dopamine make people get up and do things,
outside their conscious awareness. The number of things people do to
increase their dopamine firing rates is unlimited, neuroscientists are
discovering. Several studies were published last year looking at
monetary rewards and dopamine. Money is abstract but to the brain it
looks like cocaine, food, sex or anything a person expects is rewarding,
said Dr. Hans Breiter, a neuroscientist at Harvard. People crave it.
Some people seem to be born with vulnerable dopamine systems that get
hijacked by social rewards. The same neural circuitry involved in the
highs and lows of abusing drugs is activated by winning or losing money,
anticipating a good meal or seeking beautiful faces to look at, Dr.
For example, dopamine circuits are activated by cocaine; people become
addicted when their reward circuits have been hijacked by the drug, Dr.
Winning in gambling can also hijack the dopamine system, Dr. Berns said.
Many people visit a casino, lose money and are not tempted to go back.
But compulsive gamblers seem to have vulnerable dopamine systems, he
said. The first time they win, they get a huge dopamine rush that gets
embedded in their memory. They keep gambling and the occasional dopamine
rush of winning overrides their conscious knowledge that they will lose
in the long run.
Other experiments show that reward circuits are activated when young men
look at photos of beautiful women and that these circuits are defective
in women with eating disorders like bulimia. Bulimics say they are
addicted to vomiting because it gives them a warm, positive feeling.
Music activates neural systems of reward and emotion. Older people with
age-related impairments to the frontal cortex do poorly on gambling
tasks and, experiments show, are prone to believe misleading advertising.
Neuroscientists say that part of the appeal of live sporting events is
their inherent unpredictability. When a baseball player with two outs at
the bottom of the ninth inning hits a home run to win the game,
thousands of spectators simultaneously experience a huge surge of
dopamine. People keep coming back, as if addicted to the euphoria of
experiencing unexpected rewards.
One of the most promising areas for looking at unconscious reward
circuits in human behavior concerns the stock market, Dr. Montague said.
Economists do not study people, they study collective neural systems in
people who form mass expectations. For example, when the Federal Reserve
unexpectedly lowered interest rates twice last year, the market went up,
he said. When it lowered interest rates on other occasions and investors
knew the move was coming, markets did not respond.
Economists and neuroscientists use the same mathematical equations for
modeling market behavior and dopamine behavior, Dr. Montague said.
Neuroscience may provide an entirely new set of constructs for
understanding economic decision making.
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