Impulsiveness Linked To Activity In Brain's
Reward Center
December 29, 2006
A new imaging study shows that our brains react with varying sensitivity to
reward and suggests that people most susceptible to impulse - those who need to
buy it, eat it, or have it, now - show the greatest activity in a reward center
of the brain. The study appears in The Journal of Neuroscience.
In their study of 45 subjects, Ahmad Hariri, PhD, and colleagues at the
University of Pittsburgh and collaborators at Mount Sinai School of Medicine and
the University of Chicago showed that activity in the ventral striatum, a core
component of the brain's reward circuitry, correlated with individuals'
impulsiveness.
"These data are exciting because they begin to unravel individual
differences in brain organization underlying differences in complex
psychological constructs, such as 'impulsivity,' which may contribute to the
propensity to addiction," says Terry E. Robinson, PhD, of the University of
Michigan biopsychology program.
The Hariri team tested the subjects on two computer-based tasks. First,
participants indicated their preferences in a series of
immediate-versus-delayed, hypothetical monetary rewards. They chose between
receiving an amount from 10 cents to $105 that day and receiving $100 at one of
seven points up to five years in the future. "Switch points" - the
value at which they were equally likely to choose getting money today as getting
$100 at a future point in time - were calculated for each person.
Seven months later, subjects were told they could win money if they correctly
guessed numbers on a series of cards while scientists used blood
oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI)
to measure brain activity in response to correct and incorrect guesses. These
images reflected participants' reactions to positive and negative
"reward" feedback. After matching images to the subjects' switch
points on the index of impulsiveness, the researchers looked for patterns.
Individuals indicating the strongest preference for immediate over delayed
rewards showed the most ventral striatum activity associated with positive and
negative feedback for a monetary reward.
"Our findings suggest that the ventral striatum plays a key role in
striking a balance between gratification and delay, impulsive action and prudent
choice, that can have far-reaching implications for our current and future
well-being," says Hariri.
The team aims to examine the role of specific factors that drive the sensitivity
of the ventral striatum next. One target of future research will be genes that
regulate levels of the neurotransmitter dopamine and how they vary among
individuals, Hariri says.
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Research and investigator funding were provided by the National Institutes of
Health and the National Alliance for Research on Schizophrenia and Depression.
The Journal of Neuroscience is published by the Society for Neuroscience,
an organization of more than 36,500 basic scientists and clinicians who study
the brain and nervous system.
Contact: Sara Harris
Society for Neuroscience
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