The association between hippocampal structure and serum brain-derived neurotrophic factor (BDNF) in healthy adults: a registered report

The hippocampus is a highly plastic brain structure supporting functions central to human cognition. Morphological changes in the hippocampus have been implicated in development, aging,as well as in a broad range of neurological and psychiatric disorders.A growing body of research suggests that hippocampal plasticity is closely linked to the actions of brain-derived neurotrophic factor (BDNF). However, evidence on the relationship between hippocampal volume (HCV) and peripheral BDNF levelsis scarce and limited to elderly and patient populations. Further, despite evidence that BDNF expression differs throughout the hippocampus, and is implicated in adult neurogenesis in the dentate gyrus, no study has so far related peripheral BDNF levels to the volumes ofindividual hippocampal subfields. Besides its clinical implications, BDNF-facilitated hippocampal plasticity plays an important role in regulating cognitive and affective processes. In the current study, we will investigate how serum BDNF (sBDNF) levels relate to volumes of the hippocampal formation and its subfields in a large sample of healthy adults (N = 301, 174 f) with a broad age range (20-55 years, mean 40.7). HCV will be related to basal sBDNF and, in a subsample (n = 113, 65 f), to acute stress-reactive change in sBDNF. We will further test the role of age as a moderator of both associations. We expect a positive association of total HCV with both basal and reactive sBDNF levels. Within hippocampal subfields, we expect to find the strongest association between sBDNF and dentate gyrus volume. Further, we hypothesize the association of sBDNF and HCV to be stronger with higher age. Finally, we predict that basal and reactive sBDNF differentially relate to HCV, such that individual differences in HCV can best be predicted when using both measures jointly.