VANDERBILT (US)—Why some people are more susceptible to rash behavior and act without thinking is related to a specific deficit in the way the brain regulates dopamine signaling, according to new research.
The findings are important because impulsive personality traits are strongly associated with attention deficit/hyperactivity and antisocial personality disorders, and impulsivity is a key risk factor for developing substance abuse.
“The brain has a number of different thermostats, which sense the levels of certain brain chemicals and adjust the output of those chemicals accordingly, says Joshua Buckholtz, a PhD candidate in neuroscience working with David Zald, associate professor of psychology and psychiatry at Vanderbilt University.
“We show that one particular thermostat-like mechanism—midbrain autoreceptor regulation of striatal dopamine release—is out of whack in people with high levels of trait impulsiveness.”
Gaining a better understanding of the brain mechanisms that cause impulsivity could lead to better treatment of these disorders, which affect millions of people and cost society billions of dollars each year, according to the study that was published online July 31 in Science.
People with higher levels of impulsivity showed increased dopamine levels in a region of the brain called the striatum following the administration of the stimulant drug amphetamine.
These highly impulsive people showed lower amounts of a kind of receptor that sits on dopamine neurons in a region of the brain called the midbrain. These receptors—called autoreceptors—control the firing of the dopamine neuron, and can therefore regulate how much dopamine is present throughout the entire brain.
Buckholtz compares the regulation of dopamine by autoreceptors to the action of a thermostat:
“In your house, you have a thermostat that senses the ambient temperature and either cranks up or ramps down the activity of your furnace in response to current environmental conditions.
“The brain has a number of different thermostats, which sense the levels of certain brain chemicals and adjust the output of those chemicals accordingly. We show that one particular thermostat-like mechanism—midbrain autoreceptor regulation of striatal dopamine release—Is out of whack in people with high levels of trait impulsiveness,” he says.
As a result, too much dopamine is produced in certain regions of the brain associated with reward and motivation, at times leading to enhanced motivation to obtain rewards in impulsive individuals, who tend to seek rewards without considering the consequences of their actions, and without the ability to put the brakes on their behavior.
In addition, these data suggest that exaggerated dopamine responses to stimulant drugs may promote an especially strong craving for those drugs. This may explain why impulsive people are more likely to abuse drugs like cocaine and methamphetamine.
Better understanding the alterations in neural function that promote impulsivity might lead to improved treatments for psychiatric disorders that are characterized by high levels of impulsivity.
For example, it may be possible to use targeted drug therapies to correct the dysregulation in dopamine circuitry that results in excess dopamine in the striatum.
Certain drugs do affect the function of dopamine autoreceptors, Buckholtz says, and with further study it may be possible to use such medicines to re-regulate this circuitry to reduce levels of impulsivity.
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