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Lopez Bayo, Patricia (2007): Differences in Activation of the Visual System in Mild Cognitive Impaired Subjects compared to Healthy Subjects measured using functional magnetic resonance imaging (fMRI). Dissertation, LMU München: Medizinische Fakultät



Introduction: Mild Cognitive Impairment (MCI) is a cognitive stage between normal aging and Dementia. It is a heterogeneous group of patients, where most of them develop Alzheimer’s disease (AD), others stabilize, and a few revert to normal. AD’s first clinical symptoms are related to memory, but it has been shown that AD involves also a processing disorder in the visual sensory pathways. Accurate visual function facilitates memory, attention and executive functions, so that perceptual dysfunction contributes to the severity of cognitive impairment. Objective: The objective of the work is to measure changes in activation in the visual system between MCI patients and old Healthy Control (HC) subjects, using two different visual processing tasks with functional Magnet Resonance Imaging (fMRI). This is the first study which makes such a comparison between MCI and HC using fMRI. Methods: Brain activation was measured using fMRI. The MCI group was composed of 16 subjects and the HC group was composed of 19 subjects. All subjects performed two tasks: location matching (position of objects) and face matching (characteristics of the objects), which selectively activate one of the visual system pathways in healthy people. Answers were given by pressing a single button. Results: Performance of the task was not significantly different in both groups. The HC group selectively activated ventral pathway for face matching and the dorsal pathways for location matching. In contrast the MCI subjects did not selectively activate the ventral and dorsal pathways of the visual system. Additionally they showed higher activation in the left frontal lobe compared to HC when performing the location matching Task Conclusions: The results suggest that even when behavioural performance between groups is the same, the neural system which supports performance may differ. MCI subjects compensate their deficits using additional brain areas to help them to maintain performance. In this case MCI subjects used the left frontal lobe in addition to perform the location matching task. This work presents the usability of brain imaging techniques especially fMRI to better understand the underlying pathology of MCI and its subtypes as prodromal conditions of AD.