REM sleep behavior disorder is a parasomnia that reflects the presence of alpha-synucleinopathy in the brain and is highly predictive of eventual phenoconversion to Parkinson's disease, dementia with Lewy bodies, or multiple system atrophy over the course of years to decades. Neuroplastic adaptations in the brain during the prodromal stage of disease are thought to mask the expression of motor and non-motor signs and may substantially delay diagnosis during a potentially critical time window. This study will examine the state and progression (over 30 to 36 months) of neuroplastic changes in the excitability of the motor and prefrontal cortex (using transcranial magnetic stimulation), the structural and functional connectivity of the brain (using highfield, 7T, magnetic resonance imaging), and the relationship of these changes to the expression of motor and neuropsychological signs, in a cohort of individuals with REM sleep behavior disorder and matched controls.