PS168. Hybrid PET/MR imaging of serotonin transporter occupancy and brain activation to elucidate the mechanism of action of selective serotonin reuptake inhibitors

It has been reported that abnormalities of functional brain asymmetry was detected in patients with major depressive disorder (MDD). However, little is known about their clinical implication. The aim of this study was to examine the differences in asymmetry indexes (AIs) of hippocampus between MDD patients and healthy controls (HCs) and their relationship with cognitive functions. Forty-one patients with first-episode drug-naïve MDD and 41 agesex-matched HCs were recruited. All participants examined with 1.5T high-resolution magnetic resonance imaging. Two different methods for image analyses included manual method and FreeSurfer. Manual method was applied to analyze the longitudinal axis of hippocampal volumes, whereas FreeSurfer was used to analyze the hippocampal subfields. AIs were derived from the ratio of |left-right| to |left+right|. Cognitive functions which are composed of attention, memory, color trail test (CTT) and Wisconsin Card Sorting Test (WCST) were assessed. There were significant differences in AIs between two groups which were cornu amonis 1 (CA1) and CA4/dentate gyrus (DG). Differences in cognitive functions between groups included two sub-items in divided attention, six sub-items in word memory, one sub-item in facial memory, four sub-items in CTT and three sub-items in WCST. Partial correlation corrected by age, educational years and total intra-cerebral volume showed that there were significant correlations between CA1 and Faces1 True Positive of memory (r=-0.256, p=0.020) and Trails1 Time of CTT (r=0.226, p=0.041), CA4/DG and Faces1 True Positive of memory (r=-0.301, p=0.006) and Trails1 Time of CTT (r=0.247, p=0.025). Our results suggest AIs of CA1 and CA4/DG may play a crucial role in the cognitive dysfunction in MDD.