Depression and cognition in the elderly : neuroimaging perspective

This thesis examines the relationship between depression and brain structure in the elderly with (Study I, III) and without (Study II, IV) cognitive impairment (Alzheimer’s disease and mild cognitive impairment). Individuals from four independent cohorts were included. Participants had either a depressive episode (Study II, III) or depressive symptoms, as measured with different depression scales (Study I, IV). Studies I and II have cross-sectional design, and studies III and IV are longitudinal. Main outcomes were cortical thickness of the brain and volumes of different structures (hippocampus, ventral diencephalon, including hypothalamus and corpus callosum), or atrophy rate of the thickness and volumes (Study IV). We found in all the cohorts that depressive symptoms were associated with cortical thinning in the same region – the left temporoparietal junction. Depression-related thinning was observed in three cohorts (Studies I, IV) in superior temporal cortex and temporal pole. In two non-demented cohorts (Studies II, IV) angular cortex was also involved in depression. Longitudinal analysis revealed that thinning in these regions is secondary to depressive symptoms (study IV). In two cohorts (Study I, II) fusiform cortex was involved in depression. In study IV, we also were able to assess thinning which developed in parallel with depressive symptoms. It covered medial superior frontal cortex and lingual cortex. The number of depressive episodes was associated with cortical thinning in the left temporal pole in women (Study II) and reduced volume of the right ventral diencephalon in both – men and women (Study III). We have found moderating effect of gender on the relationship between cortical thickness and depression onset. Women with late-onset depression (>65 years) but not men had the widespread thinning in the prefrontal cortex compared to early-onset depressed. The volume of the right hippocampus and thickness of the superior frontal cortex were positively a