What’s left in face processing? Evidence from hemispheric differences in developmental prosopagnosia

Abstract

According to classic models, face processing is right-lateralized with little involvement of the left hemisphere. This is challenged by fMRI findings that developmental prosopagnosics (DP) consistently show reduced face-selective responses in the left OFA/FFA and less consistent differences in the right OFA/FFA. To account for this, we hypothesized that right hemisphere regions primarily subserve processes for face perception and, as this is highly variable in DP, we predicted that right-sided regions would only be implicated in those with greater perceptual impairment. In our sample, DPs with low performance (>1SD below controls) on at least two perceptual tests (Benton Face Recognition Test, Cambridge Face Perception Test, and face matching) were classified as perceptually impaired (N=17) and the remaining were classed as perceptually unimpaired (N=18). No controls were impaired (N=22). Using a face localizer (Faces>Objects), we found that perceptually-impaired DPs had reduced face-selective activation in both the left and right OFA, whereas perceptually-unimpaired DPs had reduced activation only in the left OFA. Both groups had reduced activation in the left but not the right FFA. Furthermore, resting-state functional connectivity between the left and right OFA was significantly reduced in perceptually-impaired but not perceptually-unimpaired DPs, consistent with neural abnormalities spanning both hemispheres in the presence of perceptual deficits. The results support the hypothesis that right hemisphere abnormalities (especially in the OFA) reflects a perceptual processing deficit that is variable in DP and explains why not all studies observe right hemisphere differences at the group level. Critically, our results suggest that left hemisphere abnormalities are common to all DPs. Although future work is needed to clarify the functional roles of the left OFA/FFA, their implication in DP suggests that they are essential for normal face recognition and are required for a complete neural model of face processing.