Memory and social interaction are intimately linked. On the one hand, social interaction is a privileged context for learning, and on the other hand, appropriate social interactions involve remembering the partners encountered and previous exchanges. People with Alzheimer's disease classic syndrome variant (AD) have a major impairment of episodic memory, while people with the semantic variant of primary progressive aphasia (SPPA) are characterized by semantic disorders in the foreground, associated with changes in their social behavior with a tendency to egocentricity. In both cases, patients frequently have reduced social interactions. Although social interaction situations seem to constitute a privileged learning context, their effectiveness for patients with cognitive disorders must be evaluated and the conditions under which they are effective must be established. The main objective of this study is to determine whether social interaction constitutes a beneficial context for learning new information and whether the presence of social behavior disorders alters this benefit. More broadly, the goal is to better understand the mechanisms underlying the possible beneficial effect of learning in social contexts and to clarify the links between memory performance in different social contexts, cognitive disorders, social behavioral changes and personality traits. Finally, a description will be made of the brain substrates associated with memory performance obtained during learning in social contexts in order to investigate their particularities. Thirty couples each including a person with AD, 16 couples each including a person with SPPA and 46 couples of persons without cognitive complaints (HC), one of which will be matched in gender and age to one of the patients, will be included in the study. Participants will perform image location learning in a grid, in three social contexts in which both members of the couple are involved: 1) simple presence of others, 2) by observation and 3) in collaboration. A psychometric assessment including social cognition and classical tests assessing memory, and questionnaires concerning global executive functioning, social behavior and personality will be offered to all participants. Patients in the AD and SPPA groups and the matched individual in the HC group will undergo anatomical and functional brain magnetic resonance imaging (MRI).