According to a study in the most recent issue of the Journal of Nuclear Medicine, certain individual personality traits—including those that govern addiction, like reward dependency—are connected to the brain’s opioidergic, or endorphine, system.

German researchers at administered Fluoro-ethyl-diprenorphine to 23 males with no history of substance abuse, then took PET scans of their brains. The scans were compared to the results of the patients’ Cloninger temperament and character inventories; these questionnaires assess personality based on novelty seeking, harm avoidance, reward dependence and persistence.

“Our main finding was that reward dependence is the only personality dimension correlated with opiate receptor binding, and that positive correlation was restricted to the ventral striatum, which is considered the key area of the human reward system and of the development of addictive behavior,” said Peter Bartenstein, MD, professor of nuclear medicine at Ludwig Maximilians-University, Munich, Germany. “This correlation means that people with high reward dependence have a high concentration of opiate receptors available in that area, while people with low dependence have fewer opiate receptors.”

The biological purpose of the brain’s “reward system” is to incentivize individuals toward behavior that is essential to survival, such as eating or reproduction. These stimuli lead to an opioid-modulated release of dopamine in core structures of the brain’s reward system.

The latest research on addiction and substance abuse suggests that genetic or acquired abuses of the reward system are what lead to addictive behavior.

“This is a novel finding and will provide a deeper understanding of the functional relation between human personality, neurobiology and addictive behavior,” said Mathias Schreckenberger, MD, professor of nuclear medicine at Johannes Gutenberg-University, Mainz, Germany. “Understanding the central role of neurotransmission processes in certain brain structures for the expression of psychologically defined constructs such as personality will make a great difference in the future of medicine. One of the more interesting aspects of this study is that it shows that PET technology is capable of detecting subtle biochemical differences in the brain in healthy persons, which may ultimately be responsible for what we consider the individual personality. This has far-reaching implications—not only for choosing the best individual treatments, but also in discussions of an individual’s free will.”

The researchers plan to further explore the neurochemistry of the human personality in subsequent studies.