Central opioidergic correlates of personality traits in healthy subjects

Abstract

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Objectives: Little is known on the neurobiological correlates of human personality. Cloninger's well-accepted biosocial model of personality describes temperaments and characters which are correlated each with distinct memory systems and neurotransmitters. Based on known contributions of the opioidergic system to rewarding processes we investigated the relation between personality traits and the opioid receptor status in healthy subjects. Methods: 23 male volunteers, after exclusion of neurologic, internal or psychiatric disorders, underwent a PET scan with the subtype-nonselective opioidergic radioligand [F-18]fluoroethyl-diprenorphine under resting conditions without sensory or cognitive stimulation. Subsequently tests for personality traits using the “Temperament and Character Inventory” (TCI) were performed. The binding potential (BP) as parameter of regional cerebral opioid receptor availability was computed by means of the modified Logan Plot using the occipital cortex as reference region. Further statistical analysis was performed using SPM2: correlations were calculated between the regional binding potential and the scores of the TCI on a voxel-by-voxel basis. Results: There was a significant (p<0.001) positive correlation between the scores of reward dependance and the BP in the bilateral ventral striatum including caudate nucleus. Another significant (p<0.001) positive correlation was found between the scores of self-directedness and the binding BP in the left orbitofrontal cortex (OFC, BA 11). Conclusions: High levels of self-directedness, critical for adaptation of behavior to fit situations in accord with chosen goals and values and involved in declarative learning, are correlated with opioid receptor binding in the OFC which is crucial to directing strategic memory processes. Reward dependance, being responsible for the maintainance of rewarding behavior and implicated in implicit memory, shows a close relation to high opioid receptor binding in the striatum which is related to reinforcement and habit learning, and thus implicating a participation of the opioidergic system in personality and associated memory processes.