Serotonin 5-HT(1A) receptor binding and self-transcendence in healthy control subjects—a replication study using Bayesian hypothesis testing

OBJECTIVE: A putative relationship between markers for the serotonin system and the personality scale self-transcendence (ST) and its subscale spiritual acceptance (SA) has been demonstrated in a previous PET study of 5-HT(1A) receptor binding in healthy control subjects. The results could however not be replicated in a subsequent PET study at an independent centre. In this study, we performed a replication of our original study in a larger sample using Bayesian hypothesis testing to evaluate relative evidence both for and against this hypothesis. METHODS: Regional 5-HT(1A) receptor binding potential (BP(ND)) was examined in 50 healthy male subjects using PET with the radioligand [(11)C]WAY100635. 5-HT(1A)availability was calculated using the simplified reference tissue model (SRTM) yielding regional BP(ND). ST and SA were measured using the Temperament and Character Inventory (TCI) questionnaire. Correlations between ST/SA scores and 5-HT(1A)BP(ND) in frontal cortex, hippocampus and raphe nuclei were examined by calculation of default correlation Bayes factors (BFs) and replication BFs. RESULTS: There were no significant correlations between 5-HT(1A) receptor binding and ST/SA scores. Rather, five of six replication BFs provided moderate to strong evidence for no association between 5-HT(1A) availability and ST/SA, while the remaining BF provided only weak evidence. CONCLUSION: We could not replicate our previous findings of an association between 5-HT(1A) availability and the personality trait ST/SA. Rather, the Bayesian analysis provided evidence for a lack of correlation. Further research should focus on whether other components of the serotonin system may be related to ST or SA. This study also illustrates how Bayesian hypothesis testing allows for greater flexibility and more informative conclusions than traditional p-values, suggesting that this approach may be advantageous for analysis of molecular imaging data.