Top-down activation of fusiform cortex without seeing faces in prosopagnosia.

Face processing can be modified by bottom-up and top-down influences, but it is unknown how these processes interact in patients with face-recognition impairments (prosopagnosia). We investigated a prosopagnosic with lesions in right occipital and left fusiform cortex but whose right fusiform gyrus is intact and still activated during face-processing tasks. P.S., a patient with a well-established and selective agnosia for faces, was instructed to detect the presence of either faces or houses in pictures with different amounts of noise. The right fusiform face area (FFA) showed reduced responses to face information when visual images were degraded with noise. However, her right FFA still activated to noise-only images when she was instructed to detect faces. These results reveal that fusiform activation is still selectively modulated by task demands related to the anticipation of a face, despite severe face-recognition deficits and the fact that no reliable stimulus-driven response is evoked by actual facial information. Healthy controls showed stimulus-driven responses to faces in fusiform, and in right but not left occipital cortex, suggesting that the latter area alone might provide insufficient facial information in P.S. These results provide a novel account for residual activation of the FFA and underscore the importance of controlling task demands during functional magnetic resonance imaging.