The face-selective ERP component (N170) is correlated with the face-selective areas in the fusiform gyrus (FFA) and the superior temporal sulcus (fSTS) but not the occipital face area (OFA): a simultaneous fMRI-EEG study

Human neuroimaging studies of face processing reveal robust and reliable face-selective responses. Event-related potential studies report that faces elicit a negative component, which peaks 170ms after stimulus onset (N170), which is higher for faces than non-face objects. Functional MRI studies typically reveal three face-selective regions in the fusiform gyrus (FFA), superior temporal sulcus (STS) and occipital face area (OFA). Despite the extensive investigation of these face-selective neural responses in the past decade, hardly any study has examined the relationship between them and no study measured them simultaneously. Given the high-temporal resolution of ERPs and the relatively high-spatial resolution of fMRI, such an investigation may shed light on possible neural sources of the N170 on one hand, and the time when information is processed by fMRI face-selective regions, on the other hand. Here we report the first simultaneous EEG-fMRI study of face processing. Faces and non-faces (chairs) were presented in a rapid-event related design. We first demonstrate that despite the major artifacts that the MR gradients generate in the EEG signal, we are able to remove these artifacts and obtain reliable face-selective N170 during simultaneous recording. Furthermore, the laterality of the N170 (the difference between its face-selectivity over the right and left electrodes) was strongly correlated with the laterality of the volume or the face-selectivity of the FFA and the STS but not the OFA. These findings are consistent with recent TMS data, which suggests that the OFA is engaged in face processing 100ms after stimulus onset, prior to the 170ms latency and with models that suggest that the OFA sends parallel inputs to the more anterior FFA and STS. These two regions may operate on different types of face information, but at the same latency of 170ms after stimulus onset.