The primary objective of this study is to characterize cerebral metabolism modifications using 18F-FDG PET technology and perfusion with 99MTC-ECD SPECT in patients with prodromal Alzheimer's Disease drawn from a high risk population. We also compare PET and SPECT imaging within this framework, and search for optimal diagnostic thresholds.

Inclusion Criteria for the group with memory problems:

• patient consulting for memory problems
• caucasian
• memory complaint is validated by a clinical evaluation
• cognitive performance is sufficiently well preserved so that a diagnostic of dementia cannot be made (according to the DSM-IV-R and NINCDS-ADRDA criteria) at the time of inclusion
• the patient speaks French
• presence of an informant
• accepts to sign consent

Inclusion Criteria for the group without memory problems (reference population):

• at least four years of formal education
• patient consulting for memory problems
• memory problem reported by the patient is not validated by the consultation, nor by the battery of tests specified during screening
• presence of an informant
• Clinical Dementia Rating (CDR) = 0
• accepts to sign consent

Exclusion Criteria:

• Instrumental Activities of Daily Living (IADL): at least two items > 1
• Anticholinesterasic treatments and/or memantin before study inclusion
• major depressive syndrome, according to the Global Depressive Scale
• Known neurodegenerative disease or general disease or major physical problems that could interfere with cognitive functioning and testing
• Pathology that might lead to death in the short term (evolving cancer, non stable cardiopathy, hepatic, renal or respiratory insufficiency)
• contra-indications for MRI, PET or SPECT scans
• not affiliated with a social security regimen

The study population consists of elderly patients over 70 years of age who consult for memory problems. These patients are further split into two groups based on the clinical validation of memory complaints.