Clarifying the functional neuro-anatomy of face perception by single-case neuroimaging studies of acquired prosopagnosia

In this paper I review the neuroimaging studies carried out over the past few years on a brain-damaged patient presenting a face-selective recognition deficit (acquired prosopagnosia), the patient PS. These studies show that (1) in rare cases such as PS, a right inferior occipital lesion damaging the occipital face area (OFA) but sparing the adjacent non-face preferential area of the ventral lateral occipital complex (vLOC) can lead to prosopagnosia without object agnosia; (2) preferential responses to faces in the fusiform gyrus (‘fusiform face area’, ’FFA’) can be observed despite a lesion encompassing the lower-level ipsilateral OFA, suggesting that there is a direct pathway in the normal brain from early visual cortices to the ’FFA’ to categorize face stimuli at the basic level; (3) while categorization of the stimulus as a face can be preserved behaviorally and in the ’FFA’ response, fMR-adaptation studies show that individual representations of faces are not extracted properly in the ’FFA’ following acquired prosopagnosia. Based on these observations, I suggest a reformulation of current hierarchical neuro-functionalmodels of face identity processing. Initial categorization of the visual stimulus as a face could take place in the right ’FFA’ following direct striate/extrastriate inputs, bypassing the OFA. This first representation would then be refined to achieve a full individual face representation, a process that depends ritically on reentrant interactions with lower-level visual reas, mainly of the right hemisphere (OFA). Altogether, the studies reviewed here illustrate how combining functional imaging and lesion studies in a single-case approach can greatly contribute to our understanding of the neuro-anatomy of face processing in the human brain.