Recognition of personally familiar faces and functional connectivity in Alzheimer's disease

Studies have reported that patients in the severe stages of Alzheimer's disease (AD) experience difficulties recognizing their own faces in recent photographs. Two case reports of late-stage AD showed that this loss of self-face recognition was temporally graded: photographs from the remote past were recognized more easily than more recent photographs. Little is known about the neural correlates of own face recognition abilities in AD patients, while neuroimaging studies in healthy adults have related these abilities to a bilateral fronto-parieto-occipital network. In this study, two behavioral experiments (experiments 1 and 2) and one functional magnetic resonance imaging (fMRI) experiment (second part of experiment 2) were conducted to compare mild AD patients (experiment 1) and moderate AD patients (experiment 2) with healthy older participants in a recognition task involving self and familiar faces from different decades of the participants' life. In moderate AD patients, variable performance allowed us to examine correlations between scores and resting-state fMRI in order to link behavioral data to cerebral activity. At the behavioral level, the results revealed that, in mild AD, self and familiar face recognition was preserved. Moreover, mild AD patients and healthy older participants showed an inverse temporal gradient, with faster recognition of self and familiar recent photographs than self and familiar remote photographs. However, in moderate AD, both self and familiar face recognition were affected. fMRI results showed that the higher the connectivity between the dorsomedial prefrontal cortex (dMPFC) and the right superior frontal gyrus (rSFG), the lower the self and familiar face recognition scores in moderate AD patients. Given that previous studies have related the superior frontal region to control processes rather than face recognition processes, these results might reflect less segregation and more interference between brain networks in AD. In other words, impaired face recognition in AD may be related to functional dedifferentiation of specific brain regions.