Prospective Memory Imaging

Inclusion Criteria : * Education level \> 7 years * Native language: French * Beck \< 7 * Medical, neurological, neuropsychological and neuroradiological depth in accordance with the criteria for inclusion and exclusion-specific population, that is to say: * Young Healthy Subjects: between 18 and 44 years old; * Middle age Healthy Subjects: between 45 and 69 years old; without memory complaints, normal performances compared to the age and the educational level for all tests of the diagnostic battery. * Elderly Healthy Subjects: over 70 years old, without memory complaints, normal performances compared to the age and the educational level for all tests of the diagnostic battery. * MCI patients: over 50 years old, presenting the current criteria for amnestic MCI including: i) memory complaint, ii) deficits of the episodic memory (lower performance of at least 1 SD from the norm for age and cultural level for one or more scores of episodic memory and iii) normal performances compared to the age and the educational level of all other cognitive functions as memory, including tests to assess cognitive abilities. * Alzheimer's patients: over 50 years old, presenting the standard criteria of NINCDS-ADRDA probable Alzheimer's disease, including abnormal global cognitive function and deficits in at least two cognitive domains identified by the diagnostic battery and a mild to moderate Alzheimer's disease (MMSE ≥ 18). Exclusion Criteria : * The sudden onset of cognitive impairments (as opposed to their slow and gradual installation in Alzheimer's disease) * A chronic neurological, psychiatric, endocrine, hepatic or infectious complaint * A history of major disease (a lung, heart, metabolic, hematologic, endocrine disease or a severe cancer); * A medication that may interfere with memory or metabolic measures * A alcohol or drugs abuse * claustrophobia, metallic object in the body * A predominantly left-hand (score below 50% in Edinburgh Inventory). * Protected adults, and persons not affiliated with a social security system will not participate in this study. * Pregnant or suckling women * The inclusion of a participant in another biomedical research protocol (during the study or within 12 months before inclusion)