On the role of the human amygdala : Mapping functions and individual variations using fMRI
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AbstractDecades of research have demonstrated a role for the amygdala in various psychiatric and neurological disorders. Still, the functional role of this brain structure and the biological mechanisms causing individual variation in amygdala function is not fully elucidated. In the present thesis we investigated a new and alternative role for the human amygdala in encoding or calculation of an event’s relevance. Amygdala activity was measured using functional MRI while subjects performed tasks encompassing high and low relevant stimuli. Secondly, we searched for biological mechanisms, i.e. gene variants, causing individual variation in amygdala functional activity by combining genome-wide data and functional imaging phenotypes from a Norwegian sample. We have made novel and important findings which imply that amygdala is important for relevance detection. Futher, we found a genome-wide significant association with a gene variant possibly affecting the expression of monoamines (i.e. dopamine and noradrenalin) within the amygdala. Thus, the individual’s response to relevant events may depend on genetic variation within monoaminergic signaling pathways. Disproportional encoding or calculation of relevance may be an important component in the observed social and cognitive impairments among patients with amygdala pathology. If so, one could speculate that pharmacological agents, which normalize amygdala function, may also reduce these impairments.
List of papers. Papers I and II are removed from the thesis due to copyright restrictions.
Paper 1 Ousdal OT, Jensen J, Server A, Hariri AR, Nakstad PH, Andreassen OA. The human amygdala is involved in general behavioral relevance detection: evidence from an eventrelated functional magnetic resonance imaging Go-NoGo task. Neuroscience 156 (2008):450-455. doi:10.1016/j.neuroscience.2008.07.066
Paper 2 Ousdal OT, Reckless GE, Server A, Andreassen OA, Jensen J. Effect of relevance on Amygdala activation and association with the Ventral Striatum. Neuroimage. 62 (2012):95-101. doi:10.1016/j.neuroimage.2012.04.035
Paper 3 Ousdal OT, Brown AA, Jensen J, Nakstad PH, Melle I, Agartz I, Djurovic S, Bogdan R, Hariri AR, Andreassen OA. Associations between variants near a monoaminergic pathways gene (PHOX2B) and amygdala reactivity: A genome-wide functional imaging study. Twin Research and Human Genetics. 13 (2012):273-85. doi:10.1017/thg.2012.5