Modulation of face processing by emotional expression and gaze direction during intracranial recordings in right fusiform cortex.

We recorded intracranial local field potentials from structurally intact human visual cortex during several face processing tasks in a patient before brain surgery. Intracranial local field potentials were measured from subdural electrodes implanted in a right fusiform region with face-sensitive activity and a more medial location in posterior parahippocampal gyrus with house-selective activity. This electrode implantation allowed us to compare neural responses with different facial properties within two adjacent but functionally distinct cortical regions. Five experiments were conducted to determine the temporal dynamics of perceptual (Experiments 1 and 5), emotional (Experiments 2 and 3), and social (Experiment 4) effects on face-specific responses in the right fusiform. Our findings showed an early negative deflection (N200) that primarily reflected category-selective perceptual encoding of facial information, whereas higher order effects of face individuation, emotional expression, and gaze direction produced selective modulations in the same face-specific region during a later time period (from 200 to 1000 msec after onset). These results shed new lights on the time course of face recognition mechanisms in human visual cortex and reveal for the first time anatomically overlapping but temporally distinct influences of identity or emotional/social factors on face processing in right fusiform gyrus, which presumably reflect top-down feedback effects from distant brain areas.