Intracerebral recordings evidence that unfamiliar face-identity recognition is supported by face-selective neural populations in the human ventral occipito-temporal cortex

In humans, the recognition of a visual stimulus as a face – generic face recognition (GFR) - and of its specific identity – face identity recognition (FIR) - are intricately linked and both functions are supported by specialized neural regions in the human ventral occipito-temporal cortex (VOTC). However, whether they are instantiated by the same or different neural populations remains unclear. On the one hand, FIR could rely largely on “different” neural populations that receives input from neural populations involved in GFR. On the other hand, FIR could rely on “shared” neural populations that support both functions potentially at different time scales. Here, we directly compared the spatio-temporal profile of the two recognition functions in a large group of epileptic patients (N=109) implanted with intracerebral electrodes in the gray matter of the VOTC. Both GFR (i.e., significantly different responses to faces vs. non-face visual objects; Jonas et al., 2016) and FIR (i.e., significantly different responses to different unfamiliar face identities; Jacques et al., 2020) neural activity was isolated with separate frequency-tagging protocols within patients. This approach provides an objective measure of the two recognition functions, parceling out general visual responses, and providing high spatial and temporal resolution. Across all the significant FIR recording contacts, we found that ~85% also showed significant GFR responses (i.e., were face-selective). This high spatial overlap was found along the posterior-anterior axis and within all core face regions. Moreover, in the overlap contacts, the amplitudes for the two functions correlated (r>.8) and the temporal onset of amplitudes for GFR and FIR was strikingly similar regardless of posterio-anterior location, but with a relatively slower build-up of the FIR amplitudes. Overall, this original dataset suggest that unfamiliar FIR is essentially supported by face-selective neural populations in the human VOTC, with GFR signals potentially transmitted faster than FIR signals.