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

Inclusion Criteria: * All subjects will be age 40 or older, * Be on stable medications for at least 30 days * Montreal Cognitive Assessment (MOCA) of 26 or higher * Scores within 1.5 standard deviations of age-matched norms for all neuropsychological tests * Parkinson's Plus Disorders (PD) will be defined using United Kingdom (UK) Brain Bank Criteria. * PD dementia (PDD) will be defined using the Movement Disorder Task Force 2007 criteria and supported by scores less than 1.5 standard deviations of age-matched norms in at least two domains. * Probable Alzheimer's Disease (AD) will be defined using the National Institute on Aging-Alzheimer Association 2011 guidelines. * Parkinson's Plus Disorders (PD) with mild cognitive impairment (MCI) will be defined by history, MOCA of 21 or higher, at least one score less than 1.5 standard deviations of age-matched norms, and cannot meet diagnostic criteria for PDD. * Essential tremor and Parkinson plus syndromes (multiple systems atrophy, corticobasal degeneration, progressive supranuclear palsy) will be defined using previously published research criteria.19-22 Exclusion Criteria * Features suggestive of other causes of parkinsonism/Parkinson-plus syndromes; * Features suggestive of other causes of dementia, including moderate to severe cerebrovascular disease by history, or imaging or history of major head trauma; * History of deep brain stimulation, ablation surgery, or other brain surgery; * Evidence for depression based on the Hospital Anxiety Depression Scale (score \> 11).