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

Investigators hypothesize that there are specific characteristic of each cognitive and motor condition that can be defined using brains scans.

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.

Eligibility Criteria:
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).