MAGNETIC RESONANCE IMAGING 3 Tesla MRI (Siemens Prisma) will be done in all study cohorts. A wide variety of magnetic resonance imaging (MRI) techniques will be used to study regional brain volume (three-dimensional magnetization-prepared rapid acquisition with gradient echo (3D MPRAGE)), metabolism (MR spectroscopy (MRS)), structural and functional connectivity of different brain regions (diffusion tensor imaging (DTI) and functional MRI (fMRI)), regional blood flow (arterial spin labeling (ASL)), iron deposition (susceptibility-weighted imaging (SWI)) and the presence of small vessel disease (MPRAGE, SWI and fluid-attenuated inversion recovery (FLAIR)). The protocol will take approximately 60 min to perform. No contrast-enhancing agent will be used.