Storage, degradation, and new connectivity of face-related semantic memory in Alzheimer's disease

Background: Excepting amnesia, impairment of other domains also hampers the activity of daily living in Alzheimer's disease (AD). Although prosopagnosia poses problem in interacting with other persons, it rarely causes problem during interaction with close relatives as known voice acts as cue for recognition. Objective: In a cohort of AD, we planned to study errors in recognition, naming, and assigning relationship of close relatives, to assess the type and frequency of errors and to explain with current knowledge and hypothesis. Materials and Methods: This cross-sectional study was conducted in Memory Clinic of Medical College Hospital, Kolkata, India, between July 2013 and June 2015. Patients were evaluated by history, general neurological examination, and neuropsychological tests. A structured questionnaire was used to assess recognition (use of honorifics) and naming defect of close relatives. Results: AD was diagnosed in 42 patients. Prosopagnosia was found in 14 and anomia in 6 patients. Four patients exhibited problem during conversation with close relatives. They assigned name and relation of one generation earlier to close relatives with proper recognitions. Discussion: We got predictive error of name and relation assignment of close relatives by one generation back with normal recognition. It can be explained by two memory traces in connection of face-visual and name (with/without relation) representation, earlier being hierarchically older and more resistant to wearing. Conclusions: We hypothesize that the name/relation store is orderly conserved. In AD, after degradation of part of name/relation store, a new wiring might be built up between these two traces.