Clarifying the functional neuro-anatomy of face processing by combining lesion studies and neuroimaging
Understanding the functional neuro-anatomy of face processing in the human brain is a longstanding goal of Cognitive Neuroscience. Up to the early 90’s, the most important source of knowledge was from lesion studies, i.e. making correlations between the localization of lesions in groups of brain-damaged patients and their face recognition impairments. The influence of Cognitive Neuropsychology, with an emphasis on single-case studies at the functional level, as well as the advent of neuroimaging studies in the healthy brain have considerably reduced the importance of lesion studies in clarifying the neuro-anatomical aspects of face processing. I will present recent studies illustrating how neuroimaging investigations of brain-damaged patients can greatly increase our knowledge of the functional neuro-anatomy of face processing. Neuroimaging studies have shown that the middle fusiform gyrus (MFG) and the inferior occipital gyrus (IOG) are activated by both detection and identification of faces. We acquired functional magnetic resonance imaging (fMRI) data during face processing in a brain-damaged patient presenting a specific deficit in individual face recognition, following lesions encompassing the right IOG but sparing the right MFG. In a first study (Rossion et al., 2003), we observed a normal sensitivity to faces (vs. Objects) in the right MFG, demonstrating that it does not need inputs from the rIOG, as hypothetized previously (Haxby et al., 2000). In a second study (Schiltz et al., 2005), we used an adaptation paradigm to show that the fMRI signal in the rMFG of the patient does not differ between conditions presenting identical and distinct faces, in contrast to the larger response to distinct faces observed in the normal brain. These results suggest that normal individual discrimination of faces critically depends on the integrity of both the rMFG and the rIOG, which may interact through re-entrant cortical connections.