Face recognition deficits in a patient with Alzheimer’s disease: amnesia or agnosia?

Face recognition difficulties are frequently reported in Alzheimer’s
disease (AD) and often attributed to memory impairment. However, it has
been hypothesized that failure in identifying familiar people could also
be due to deficit in higher-level perceptual processes since there is
evidence showing a reduced inversion effect for faces but not for cars
in AD. To address the involvement of these higher processes, we
investigated ERP neural correlates of faces in an AD patient. AD patient
MCG showing a face recognition deficit participated in the EEG study.
Eight healthy participants were tested as control group. Participants
performed different tasks following stimulus presentation. In experiment
1, they should indicate whether the stimulus was either a face or a
house, or a scrambled image. In experiments 2 and 3, they should
discriminate between upright and inverted faces (Experiment 2: faces
with neutral or fearful expressions; Experiment 3: famous or unfamiliar
faces). Electrophysiological results reveal that the typical
face-specific modulation of the N170 component, thought to reflect the
structural encoding of faces, was not present in MCG, despite being
affected by the emotional content of the face implicitly processed by
MCG. Conversely, the N400 component, thought to reflect the recruitment
of the memory trace of the face identity, was found to be modulated
implicitly in MCG. These results suggest a possible role of gnosic
processes in face recognition deficits in AD.