Depression in the Elderly and Cerebral Amyloid Plaques: Characterization by [18F] AV-45 Affectives Symptoms and Amyloïd Plaques (ASAP)

Inclusion Criteria * Adult 55 years or older * Native language : french * Study period \> 7 years * Major depression defined on the DSM-IV criteria assessed by MINI and HDRS score of 10 or over * Affiliation to the national health insurance system * Signed informed consent Exclusion Criteria * History of alcoholism or drug addiction * MMSE less than or equal to 17 * Major depression with psychotic features * Depressive episode resistant, patient who received two different antidepressants well conducted without significant therapeutic response * Any current or past episode of mania, schizophrenia or any other psychotic disorder * Any past history of stroke or Parkinson's disease * Any current significant unstable illness * Any past diagnosis of Alzheimer's disease * Any current treatment by AcethylCholinesterae inhibitor, memantine or antidepressant therapy. * Contraindications to MRI in patients with: 1. Metallic foreign body eye. 2. Any implanted electronic medical irremovably (pacemaker, neurostimulator, cochlear implants ...) 3. Metal heart valve, 4. Vascular clips formerly located on cranial aneurysm. * Contraindications to antidepressants * History of progressive disease that can affect the central nervous system such as uncontrolled diabetes, blood pressure greater than or equal to 180/100; chronic lung disease with hypoxia, head trauma with loss of consciousness greater than or equal to 15 minutes; brain surgery, encephalitis, recently treated cancer (\<1 year), altered cerebral metabolism including subjects with stroke sequelae extended. Patients with lacunar stroke without thalamic or striatal may be included.