An electrophysiological endophenotype of hypomanic and hyperthymic personality.

BACKGROUND: Hyperthymic Temperament (HYT) and a closely related trait, Hypomanic Personality (HYP), have both been related to bipolar affective disorder (BAD). Intensity dependence of auditory evoked potentials (IAEP) is a suggested inverse indicator of serotonergic neurotransmission and has been found to be elevated in BAD. Therefore the present study explored for the first time whether subclinical variance of HYT/HYP is also associated with IAEP in a healthy sample. As several traits from biological personality research are correlated with HYT/HYP and also with BAD, the specificity of results against these traits was further analyzed by calculating multiple regression analyses. METHODS: Evoked potentials were recorded from a sample (N=87) homogenous for confounding variables influencing IAEP. For this reason, only 19 to 27-year-old non-smoker psychiatrically healthy male students were included. RESULTS: Significant correlations were found between IAEP and both HYP and HYT. Including Sensation or Novelty Seeking and Extraversion in Regression Analyses did not weaken the associations of HYP with IAEP much, but did affect those of HYT. However, these competing biological personality traits were hardly able to predict IAEP themselves. Impulsivity, though, was able to reduce the predictive power of HYP and HYT and to explain unique IAEP-variance. This was even more the case for Behavioral-Activation-System-Sensitivity (BAS) subscale Fun Seeking clearly dominating all regression analyses. LIMITATIONS: Homogeneity of sample. CONCLUSIONS: The impact of BAS is in agreement with the assumption that heightened BAS-sensitivity is an underlying biological cause for HYP/HYT and for BAD. Future studies on BAD should include BAS and Impulsivity besides HYP/HYT to further explore uniqueness of the latter and to develop questionnaires based on those items of a hyperthymic-hypomanic-impulsive-funseeking item pool, which possess the most external validity.