for depressed patients :subject with a diagnosis of depression confirmed by a psychiatric evaluation and MADRS (Montgomery and Asberg Depression Rating Scale) score \>25 and without cognitive impairment or any other psychiatric pathology and MMSE (Mini Mental State Examination)≥18 and without symptoms of AD
for Alzheimer patients :subject with AD diagnosed according to NINCDS-ADRDA (National Institute of Neurological and Communicative Disorders and Stroke -Alzheimer's Disease and Related Disorders Association) criteria and MMSE ≥18 and without psychiatric disorder and MADRS score \< 25
for control patients : subject without AD, depression or any other psychiatric condition identified by the diagnostic criteria or cognitive disorders and MADRS score \<25 and MMSE \> 20
