Inclusion Criteria - Neurodegenerative Disease and Disorders :

• Age and gender matched to healthy participants with no known neurodegenerative disorder.
• Absence of primary psychoses including schizophrenia, bi-polar disorder or other (patients with co-morbid depression can be included)
• Ability to give, with or without caretaker, verbal or written consent.
• Currently diagnosed with AD, PDD, DLB, or MCI [(McKhann et al., 2011) (Emre et al., 2007), (McKeith et al., 2017), (Albert et al., 2011)] .

Exclusion Criteria - Neurodegenerative Disease and Disorders:

• Recent (past 5 years) head injury, or older head injury with current symptoms.
• Regular (daily) use of opiate pain medications.
• Any eating disorders (anorexia, bulimia).
• History of marijuana/cannabis use (amount/ times per week).
• Excessive tobacco use (i.e. more than 10 cigarettes a day).
• Excessive alcohol (> 5 drinks daily) or caffeine (>10 cups daily).
• Any known clinically significant pulmonary (lung) disorders.
• Untreated/untreatable vision or hearing problems.
• Pregnant or nursing.
• Inadequate familiarity with the English language.
• Older than 90 years of age or younger than 40 years of age.

Inclusion Criteria - Healthy Controls:

• Age and gender matched to patients diagnosed with neurodegenerative disorder.
• Absence of a neurological or psychiatric illness.
• Ability to give verbal and written consent.

Exclusion Criteria - Healthy Controls:

• Any known sleep disorder (e.g., narcolepsy, severe sleep apnea, chronic insomnia).
• Recent (past 5 years) head injury, or older head injury with current symptoms.
• Regular use of opiate pain medications.
• Any eating disorders (anorexia, bulimia).
• Current use or a history of use of stimulants (e.g., amphetamine) or substance abuse.
• History of marijuana/cannabis use (amount/ times per week).
• Excessive tobacco use (i.e. more than 10 cigarettes a day).
• Any known neurological or psychiatric illnesses.
• Excessive alcohol (> 5 drinks daily) or caffeine (> 7 cups daily).
• Any known clinically significant pulmonary (lung) disorders.
• Untreated/untreatable vision or hearing problems.
• Pregnant or nursing.
• Inadequate familiarity with the English language.
• Older than 90 years of age or younger than 40 years of age.

Exclusion Criteria - All Participants:

• Heart failure (i.e., myocardial infarction).
• Epilepsy (current episodes and medication in the past year).
• Known AIDs (HIV+) diagnosis
• Bipolar disorder.
• Severe/psychotic depression requiring immediate psychiatric hold because of danger to self or others. 

PSG SubStudy Only:

Inclusion Criteria - REM sleep behavior disorder:

• Fulfill criteria for RBD based on polysomnography according to the standard International Classification of Sleep Disorders diagnostic criteria, 3rd edition (American Academy of Sleep Medicine 2014).
• Age and gender matched to healthy participants with no known neurodegenerative disorder.

Exclusion Criteria - (REM sleep behavior disorder):

• Recent (past 5 years) head injury or older head injury with current symptoms.
• Inadequate familiarity with the English languageepilepsy (current episodes and medication in the past year).
• Known AIDs (HIV+) diagnosis.
• Severe/psychotic depression requiring immediate psychiatric hold because of danger to self or others.

Inclusion Criteria - Healthy Controls:

• Age and gender matched to patients diagnosed with REM sleep behavior disorder.
• Absence of a neurological illness.
• Ability to give verbal and written consent.

Exclusion Criteria - Healthy Controls:

• Any known neurological illnesses.
• Iadequate familiarity with the English language.
• Known AIDs (HIV+) diagnosis.
• Severe/psychotic depression requiring immediate psychiatric hold because of danger to self or others. 

• Patients will not be excluded for controlled hypertension, diabetes, high cholesterol, mild to moderate sleep apnea or depression.
• Medical marijuana use will not be a cause for excluding a participant; however, current use will be documented.