This project will provide a comprehensive picture of the effects of mild hypo- and hyperthyroidism on higher cognitive function, white and grey brain matter structure, brain functional connectivity and brain perfusion, by using state of the art multimodal neuroimaging and neurocognitive testing. Such a data base is necessary for the understanding of the scope of thyroid hormone action in the CNS. Moreover, using an existing extensively phenotyped (cognitive functions, personality, imaging) cohort, we will assess the effects of genetic differences in thyroid hormone transporters (polymorphisms of MCT8) on the central availability of thyroid hormones indexed by cognitive function and brain structural measures.