Neural Coding of Individual Faces in the Human Right Inferior Occipital Cortex: Direct Evidence from Intracerebral Recordings and Stimulations

Abstract

Discriminating individual faces requires elaborate and refined perceptual skills call for by few other categories of objects. Yet, the neural basis of individual face coding in the human brain remains unknown. Here we were able to test for behavioral individual discrimination during transient inactivation of a face-selective area of the right inferior occipital gyrus ("occipital face area", OFA) in an epileptic patient implanted with intracerebral depth electrodes (patient KV described in Jonas et al., 2012). During electrical intracerebral stimulations of the rOFA, KV was presented with pairs of identical or slightly different (40%) morphs of unknown faces and was asked to tell if the 2 faces were different. Outside stimulations, she was almost flawless (49/54 trials). However, when stimulating one electrode contact (D5) in the rOFA (movies available), her performance dropped to 0% (0 of 6 trials). She clearly stated that there were no visual distortions that disturbed the task. Face-selective ERPs and gamma-ERSP responses were found at this contact, which was located within the rOFA defined in fMRI. Most importantly, evidence for strong sensitivity to individual faces was found at the contact D5 using fast (6 Hz) periodic visual stimulation of blocks of different or identical individual faces (Rossion & Boremanse, 2011). This effect was observed only at a few contiguous electrode contacts, but of all contacts (27 in the right ventral occipito-temporal cortex), the largest difference between the effect for upright and inverted faces was observed at D5. These findings provide the first evidence of transient impairment of individual face discrimination following electrical intracerebral stimulation, and point to a critical functional role of the right OFA in individual face perception (Schiltz & Rossion, 2006). These observations also support the functional relevance of visual adaptation effects obtained with high-level visual stimuli through fast periodic visual stimulation.

Meeting abstract presented at VSS 2013