Covert face recognition without the fusiform-temporal pathways.

Patients with prosopagnosia are unable to recognize faces consciously, but when tested indirectly they can reveal residual identification abilities. The neural circuitry underlying this covert recognition is still unknown. One candidate for this function is the partial survival of a pathway linking the fusiform face area (FFA) and anterior-inferior temporal (AIT) cortex, which has been shown to be essential for conscious face identification. Here we performed functional magnetic, and diffusion tensor imaging in FE, a patient with severe prosopagnosia, with the goal of identifying the neural substrates of his robust covert face recognition. FE presented massive bilateral lesions in the fusiform gyri that eliminated both FFAs, and also disrupted the fibers within the inferior longitudinal fasciculi that link the visual areas with the AITs and medial temporal lobes. Therefore participation of the fusiform-temporal pathway in his covert recognition was precluded. However, face-selective activations were found bilaterally in his occipital gyri and in his extended face system (posterior cingulate and orbitofrontal areas), the latter with larger responses for previously-known faces than for faces of strangers. In the right hemisphere, these surviving face selective-areas were connected via a partially persevered inferior fronto-occipital fasciculus. This suggests an alternative occipito-frontal pathway, absent from current models of face processing, that could explain the patient's covert recognition while also playing a role in unconscious processing during normal cognition.