31 December 2008

Novelty Seeking Linked To Dopamine System

Earlier work has suggested that a propensity for risky behaviors, like driving fast cars, gambling and drinking, is influenced by dopamine, one of the brain’s chemical messengers. Now a team of researchers led by neuroscientist David Zald has confirmed in humans a link between “novelty-seeking personality traits” and dopamine receptors. The team’s results appear in the Dec. 31 Journal of Neuroscience.

“Risk seeking is a basic characteristic that varies widely among people,” says Zald, of Vanderbilt University in Nashville. . . .

Nerve cells excrete and detect dopamine to communicate with the rest of the brain. The chemical controls diverse brain functions — motor control, sleep and pleasure have all been linked to dopamine signaling. A nerve cell detects dopamine released from other nerve cells or from itself through proteins on the outside of the cell called dopamine receptors, which come in many varieties. . . .

To get a better idea about dopamine regulation in thrill-seeking humans, Zald’s team asked 34 healthy adult men and women a battery of questions to determine whether the people were prone to engage in risky behavior. Among other things, the subjects were asked whether they enjoy exploring new situations, make decisions rashly, buy expensive things and feel unconstrained by rules. The higher the score on the novelty-seeking scale, the greater the drive for novelty — which often leads to risky behavior.

Using PET, or positron emission tomography, to scan the volunteers’ brains, the researchers could track the location of an injected chemical that binds to two kinds of dopamine receptors, D2 and D3. The tracer signaled the presence of the dopamine receptors. Subjects who scored higher on the novelty-seeking scale had significantly fewer dopamine receptors in the ventral midbrain region. . . .

When some receptors bind dopamine, they prevent the cells they reside on from releasing more of the chemical in what’s called a negative feedback loop. Since risky people have fewer of these dopamine-dampening receptors, they have fewer checks on dopamine levels. “When stimulated, high novelty seekers release more dopamine, and get a greater reinforcement,” says Zald.

From Science News.

The study did not address why people have different dopamine responses, a classic nature v. nuture question. Heritability estimates based upon twin studies suggest that about 32% of the variation in the trait is attributable to genetic inheritance. See also, e.g., Feeling Good By C. Robert Cloninger at page 292, making it one of the more strongly inherited traits on a seven dimensional Temperament and Character Inventory (in the context of a discussion of epigenetics).

General background on the dopamine system's role in the brain can be found here.

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