Defining Phenotypes of Movement Disorders :Parkinson's Plus Disorders (PD), Essential Tremor (ET), Cortical Basal Degeneration (CBD), Multiple Systems Atrophy (MSA), Magnetoencephalography.

Specific Aim 1: Determine which features of resting Magnetoencephalography (MEG) brain activity most sensitively discriminate between PD with normal cognition, PD with mild cognitive impairment (MCI), and PD dementia (PDD). Investigators predict that frontal network slowing and connectivity will discriminate between normal cognition and MCI while visuospatial network involvement will distinguish the PDD group. Specific Aim 2: Determine which features of resting MEG brain activity most sensitively discriminate PDD from Alzheimer's Disease. Investigators predict that PDD will be distinguished from Alzheimer's (AD) on the basis of increased network connectivity, particularly in frontal and visuospatial networks. Specific Aim 3 Investigate how resting state MEG activity correlates with task related brain activity. Investigators predict that resting state slowing will be associated with decreased task related brain activity. Specific Aim 4: Determine which features of resting MEG brain activity most sensitively discriminate between motor subtypes of PD and also other relevant clinical populations (essential tremor and Parkinson plus syndromes). Investigators predict that frontal and parietal slowing and connectivity will discriminate PD from related conditions and that patterns of motor cortex connectivity and activity will differentiate among PD motor phenotypes.