Poster | Affektive Störungen P24 Altered structural corticosubcortical connectivity in major depression dependent on symptom severity A. Osoba, J. Haenggi, D. Horn, J. Kaufmann, U. Eckert, K. Zierhut, K. Schiltz, J. Steiner, B. Bogerts, M. Walter, Magdeburg Introduction: Diffusion Tensor Imaging (DTI) can be used to study white matter fiber tracts by measuring the movement of water molecules (Behrens et al.2003, Mukherjee et al.2008). It is known that Major Depressive Disor<strong>der</strong> (MDD) is associated with microstructural brain abnormalities and changes in white matter (Kieseppä et al.2009, Li et al.2007). Recent studies could show differences in functional connectivity in the hippocampus, amygdala, dACC and prefrontal cortex between MDD patients and healthy controls (Greicius et al.2007). The aim of this study was to find anatomical correlates of the functional differences found in fMRI and the differences in functional connectivity in MDD patients. We presumed that a decrease in fractional anisotropy (FA), as a sign of disintegration of white matter tracks can be found in MDD patients located in cortical and subcortical regions playing an important role in affective states and behaviors. Methods: DTI datasets of 20 patients with a major depressive disor<strong>der</strong> (MDD) and 20 healthy controls were analysed. Diffusion Tensor Imaging was performed on a 3 Tesla GE scanner using the following parameters: TR=8200ms, TE=89ms, FOV=256mm in width and height and a slice thickness of 2 mm. Diffusion was measured in 12 directories. Cortical and subcortical regions of interest representing areas found as affected in depression were defined according to functional MRI studies during task and rest on individual brains. The FA values within these ROIs as well as their interconnecting fibertracts were tested for differences between depressive patients and healthy controls. Data analysis was performed using FSL, SPM5 and SPM8. Depression severity was ascertained by using the Hamiton Depression Rating Scale (HDRS) and the Montgomery-Asberg Depression Rating Scale (MADRS). Results: Comparing MDD patients and healthy controls we found decreased FA values in depressive patients not only on whole brain level but also in those regions showing functional differences un<strong>der</strong> taskcondition namely the dACC, corpus callosum and the pgACC. Specific effects of group were further found for fiber tracts connecting these cortical and the subcortical target regions: Significant decreases of the FA values in MDD patients were measured in one of these white matter ROIs namely between the centromedian nucleus of the thalamus and the left amygdala. In addition severely depressed patients with higher scores in the MADRS show significantly lower FA values in different white matter ROIs. Correlations between HDRS and FA values un<strong>der</strong>line the role of depression severity in structural brain abnormalities. Moreover we are interested in correlations between cortical thickness and fractional anisotropy and functional connectivity and structural changes in white matter. We will present first results. Conclusion: Our study shows that white matter integrity is reduced in MDD patients on whole brain level, reflecting a reduced integrity especially in those regions also showing functional differences un<strong>der</strong> taskcondition. For the first time we could reveal thalamocortical projections involving those regions show a significant reduction in fractional anisotropy in MDD population compared with healthy controls, when anatomically defined thalamic subregions with known differential projections to the cortical target regions are chosen. Our results suggest anatomical correlates for functional deficits in emotional and cognitive processing in depressed patients and contribute to a complex un<strong>der</strong>standing of thalamo-cortical circuits in depression. These anatomical differences provide a new pattern to characterize patients with major depressive disor<strong>der</strong> and might be used for diagnostic and therapeutical classification. So we provide a further evidence, that inter-individual differences in functional MRI reflect anatomical variability. References: Behrens, T.E.J. (2003), ‘Non-invasive mapping of connections between human thalamus and cortex using diffusion imaging’, Nature Neuroscience, vol.6, no.7, pp. 750-757 Greicius, M. (2007), ‘Resting-State Functional Connectivity in Major Depression: Abnormally Increased Contributions from Subgenual Cingulate Cortex and Thalamus’, Biol Psychiatry, no.62, no.5, pp. 429–437 Kieseppä, T. (2009), ‘Major depressive disor<strong>der</strong> and white matter abnormalities: A diffusion tensor imaging study with tract-based spatial statistics’, Journal of Affective Disor<strong>der</strong>s, vol. 120, no.1-3, pp. 240-244 Li, L. (2007), ‘Prefrontal white matter abnormalities in young adult with major depressive disor<strong>der</strong>: A diffusion tensor imaging study’, Brain Research, vol.1168, pp.124-128 8. <strong>Mitteldeutsche</strong> <strong>Psychiatrietage</strong> | 86
Mukherjee, P. (2008), ‘Diffusion Tensor MR Imaging and Fiber Tractography: Theoretic Un<strong>der</strong>pinnings’, American Journal of Neuroradiology, vol. 29, no.4, pp.632-641 8. <strong>Mitteldeutsche</strong> <strong>Psychiatrietage</strong> | 87
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