Functional Anatomy of Face Processing in the Primate Brain

National Institute Of Mental Health

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Abstract

Lesions of inferior temporal (IT) cortex in humans can result in the syndrome termed prosopagnosia, an inability to recognize familiar faces. Single-cell recordings from IT cortex of monkeys have revealed the existence of neurons that are selectively activated by visual images of faces. Additionally, fMRI of both human and monkey brains has demonstrated face-selective regions, in which the fMRI signal evoked by faces is greater compared to that evoked by non-face objects. Together, these studies point to specialized neural machinery in the primate brain for processing faces. Thus far, our group and others have shown that the neural circuitry for face processing consists of a network of brain regions in the temporal and prefrontal cortex as well as in the amygdala. During the past year, we have made a number of important discoveries regarding the neural mechanisms mediating face processing: 1. FMRI activation at 7T showed that the enhanced response to fearful relative to neutral faces in the primary visual cortex was confined to the superficial layers, consistent with the idea that the processing of facial valence in visual cortex is mediated through feedback projections from the amygdala. 2. Granger causality analysis of MEG data revealed that, during configural face processing but not during featural face processing, dorsal stream visual areas send information to ventral stream visual areas, indicating that visuospatial information is transmitted from parietal cortex to ventral face-processing regions during configural face processing. 3. The results of an fMRI adaptation paradigm showed that changes in facial expression and changes in head orientation engage separate neural substrates within the superior temporal sulcus of macaques, indicating a division of labor within the network of brain regions specialized for processing faces. 4. Behavioral and fMRI results showed that individuals with Moebius Syndrome, a rare genetic disorder characterized by facial paralysis, leads to a specific impairment in processing facial expressions, such that their inability to produce facial expressions dampens their perception of these expressions. 5. FMRI results showed that body selective regions in the macaque brain responded more to images of fearful bodies than neutral bodies when the stimuli belonged to either macaques or humans but not a species that the subjects had no previous real-world experience with.