Functional Asymmetry Of The Prefrontal Cortex And Structural Disconnectivity Of The Corpus Callosum In Medication Naive Patients With Major Depressive Disorder

Chapter 1 Functional asymmetry within the prefrontal cortex in medication naive patients with major depressive disorderOBJECTIVE:The abnormalities in the functional balance between the left and right prefrontal cortex (PFC) are implicated in pathophysiology of major depressive disorder (MDD). The aim of the study is to explore the asymmetry of functional connectivity between the PFC and amygdala in medication naive patients with major depressive disorder (MDD), using functional magnetic resonance imaging (fMRI) technique with happy, fearful and neutral facial emotion stimulation.METHODS:fMRI scans were obtained from 28 medication naive MDD patients and 33 well-matched healthy controls. All participants were asked to complete a task with three types of facial emotion stimuli during the scan. fMRI images were firstly preprocessed with SPM5 software package. Using self-developed software, correlation coeffience maps were obtained for each participant within three different conditions with bilateral amygdala as seed regions. Analyss of variance (ANOVA) for each condition was performed on a voxel-by-voxel basis between the two groups.RESULTS:With fearful facical emotion stimulus, medication naive MDD patients showed significantly decreased functional connectivity between the left ventromedial prefrontal cortex (vmPFC) and amygdala compared to healthy controls; no significant difference was found in the right wmPFC. By contrast, with happy and neutral facial emotion stimuli, there was no significant difference in the bilateral PFC between the two groups.CONCLUSIONS:The findings demonstrate functional asymmetry of the left and right PFC involved in emotional dysregulation of MDD. Specifically, functional asymmetry between vmPFC and amygdala may play more important role in fearful emotion processing and regulation in MDD patients. Chapter 2 The corpus callosum integrity in medication naive adult patients with major depressive disorderOBJECTIVE:Abnormalities in the anterior interhemispheric connections provided by the corpus callosum (CC) have long been implicated in major depressive disorder (MDD). The aim of this study was to explore the interhemispheric connectivity in adult patients with MDD by measuring fractional anisotropy (FA) in the CC with diffusion tensor imaging (DTI) technique.METHODS:Diffusion tensor imaging scans were obtained from 27 medication-naive adult patients with MDD and 27 matched healthy controls. FA values were compared between the two groups using semi-automatic region of interest methods to localize the regional CC differences between the groups.RESULTS:FA values were significantly lower in the anterior genu of the CC in the MDD group than the healthy control group (p<0.05, corrected); No significant difference in FA values was found in any other subregions.CONCLUSIONS:The findings demonstrate abnormalities in the structural integrity of the anterior genu of the CC in medication-naive adult patients with MDD, which may contribute to impairment of interhemispheric connectivity in this disorder.