Dissociation between recognition of familiar scenes and of faces in patients with very mild Alzheimer disease: An event-related potential study

Objective: We used event-related potentials (ERPs) to examine the recognition of familiar faces and scenes in patients with very mild Alzheimer disease (VMAD). Methods: Two types of stimuli, FACEs and SCENEs, and two versions of each type, FAMILIAR and NOVEL, were presented. Three ERPs were compared between VMAD and normal control (NC): (1) P100 to examine basic visual processing, (2) N170 structural encoding, and (3) N250r familiarity. Results: A prominent N170 was elicited by FACEs in P8 and the largest N170 by SCENEs in P3 and P4. Participants had more errors when judging pictures of SCENEs as familiar or not than that of FACEs. In P3 and P4, NC produced larger N170 than VMAD. From N250r in F3, the familiarity effect was absent in VMAD when familiar scenes were provided. This deficit was not seen in processing familiar faces. Conclusions: This study shows that different neural regions are responsible for the early visual processing in the structural encoding of scenes and faces. The pattern of P100 and that of N170 suggest that VMAD patients maintain basic visual processing and structural encoding abilities. A conflict between behavioral and physiological responses may play a role in VMAD patients' risk of getting lost in familiar environments. Significance: Scene recognition is impaired earlier than face recognition in the course of Alzheimer disease. (C) 2010 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.