Nature Or Nurture: Are You Who Your Brain Chemistry Says You Are?

ScienceDaily (Aug. 13, 2008) — Researchers using positron emission tomography (PET) have validated a long-held theory that individual personality traits—particularly reward dependency—are connected to brain chemistry, a finding that has implications for better understanding and treating substance abuse and other addictive behaviors.

In a study to identify biochemical correlates of personality traits in healthy humans, researchers focused their investigation for the first time on the role of the brain’s opioidergic (or endorphine) system—specifically, the connection between an individual’s level of reward expectancy and the brain’s ability to transmit naturally occurring opiates. The study included 23 males with no history of substance abuse who were administered Fluoro-ethyl-diprenorphine—a radiolabeled chemical that binds readily to the brain’s naturally occurring opiate system— and then underwent a PET scan.

The scans were compared to the results of each participant’s Cloninger temperament and character inventory, a questionnaire that assesses human personality based on four dimensions: novelty seeking, harm avoidance, reward dependence and persistence. The comparison revealed that the binding to opiate receptors in the ventral striatum—an area of the brain known to be a central part of the reward system—correlated narrowly to the individual degree of reward dependence. The participants who skewed toward a high need to feel rewarded by approval were also those with the highest uptake of opiates, or endorphins, in the reward system.

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