Heterogeneous structure in face-selective human occipito-temporal cortex

It is well established that the human visual system contains a distributed network of regions that are involved in processing faces, but our understanding of how faces are represented within these face-sensitive brain areas is incomplete. We used fMRI to investigate whether face-sensitive brain areas are solely tuned for whole faces, or whether they contain heterogeneous populations of neurons tuned to individual components of the face as well as whole faces, as suggested by physiological investigations in nonhuman primates. The middle fusiform gyrus (fusiform face area, or FFA) and the inferior occipital gyrus (occipital face area, or OFA) produced robust BOLD activation to synthetic whole face stimuli, but also to the internal facial features and head outlines. BOLD responses to whole face stimuli in FFA were significantly reduced after adaptation to whole faces, but not after adaptation to features or head outlines, whereas activation to head outlines was reduced after adaptation to both whole faces and head outlines. OFA showed no significant adaptation effects for matching adaptation and test conditions, but did exhibit cross-adaptation between whole faces and head outlines. The internal face features did not produce any significant adaptation within either FFA or OFA. Our results are consistent with a model in which independent populations of whole face-, feature-, and head outline-tuned neurons exist within face-sensitive regions of human occipito-temporal cortex, which in turn would support tasks such as viewpoint processing, emotion classification, and identity discrimination.