Subjects will be referred from dementia/Alzheimer's Disease clinical patients at study sites.

Inclusion Criteria:

1. Subject is between 18 and 90 years of age
2. i. Provide written informed consent for study participation, OR ii. Provide written assent to study participant accompanied by the provision of written informed by the subject's legally authorized representative (LAR); see Section 8. Informed Consent for details of the procedures use to meet these study inclusion criteria

3. Have one of the following clinical diagnoses or conditions:

   • Probable AD according to the NINCDS-ADRDA criteria
   • Possible AD according to the NINCDS-ADRDA criteria
   • Prodromal AD according to criteria described by Dubois & Albert (2004)
   • Normal control subject

Exclusion Criteria:

1. Have a significant non-AD neurological condition including Parkinson's Disease, Vascular Dementia, Lewy Body Dementia or Frontal Temporal Dementia, human immunodeficiency virus, multiple sclerosis, epilepsy, or severe traumatic brain injury.
2. Have dementia due to multiple etiologies (e.g. mixed dementia)
3. Show the presence of prominent disturbances in gait thought to be associated with Parkinsonism.
4. Show prominent changes in personality or social conduct prior to the onset of prominent cognitive dysfunction
5. Have a Modified Hachinski Ischemia Scale score of greater than 4
6. Have a history of primary psychotic disorder (e.g schizophrenia, schizoaffective disorder, delusional disorder) or bipolar disorder
7. Have a lifetime or current history of alcohol or substance abuse/dependence
8. Have had an MRI two weeks prior to completing the MEG scan
9. Have metal braces or pacemaker that may interfere with the MEG scan
10. Are unable to complete the MEG scan procedure

Follow-up Assessment Inclusion Criteria:

Subjects who completed Protocol ADG 08-01 will be contacted and invited to participate in the follow-up assessment.