The primary objectives are to assess if there is an increase in the apparent diffusion coefficient (ADC) in the human brain during sleep when compared to the awake state and to determine if they vary across brain regions. Secondary outcomes are to assess inter subject variability in the differences in ADC between awake and sleep. We will also run exploratory analysis to determine if ADC changes with sleep are associated with subjective perception of rested sleep and to assess if there are differences in T1 in CSF between the scan taken prior to falling asleep and those taken shortly after waking up.