A critical role of the right fusiform gyrus in individual face discrimination: Evidence from neuroimaging studies of a prosopagnosic patient

Abstract

Prosopagnosic patients cannot recognize and discriminate individual faces, but they are generally still able to identify faces amongst other objects (“it's a face”). In other words, they are capable of solving tasks that rely on processing faces at the basic category level, but they are impaired when they have to use the individual subordinate level. Recently, we showed normal activation of the right middle fusiform gyrus (the ‘fusiform face area’, FFA) in response to faces compared to objects in a brain-damaged prosopagnosic patient (PS, Rossion et al., 2003), despite her selective deficit in recognizing faces and a lesion to the right posterior visual cortex. In the present study, we used fMR-adaptation (Grill-Spector and Malach, 2001) to test whether the right FFA in this patient carried information about individual face perception. PS and nine normal control subjects (2 age-matched) were scanned while viewing alternative blocks of identical and different faces. When viewing different faces as compared to viewing identical faces (in 3 runs), all control subjects showed a strong recovery from adaptation in the FFA, as described previously (e.g. Gauthier et al., 2000). PS was scanned three times (9 runs in total) and her right FFA also showed a small recovery from adaptation, but the effect was much weaker and systematically smaller than in all normal control subjects. The diminished recovery from adaptation was confirmed using a rapid event-related design adapted from Kourtzi and Kanwisher (2001) to face processing. This neuronal response pattern matches with PS's behavioral abilities in face individual discrimination, which are better than at chance but significantly worse than in normal age-matched controls. These results suggest that neurons in the right FFA play a crucial role in identifying faces at the individual level, a function that is critically impaired in brain-damaged prosopagnosic patients.