Cortical neurodynamics of face processing assessed by MEG

Face processing has been studied using various neuroimaging techniques which revealed activation of different cortical areas but the dynamics of the brain networks involved are not fully understood. Magnetoencephalography (MEG) is well-suited to investigate different stages in face perception for its millisecond temporal resolution. We used MEG measurements and spatio-temporal source analysis to estimate locations and sequence of activation of the brain regions involved in processing of face stimuli (Fig.1). We were particularly interested in the earliest face-related cortical responses. Our data demonstrated differences in responses to face and object already about 100 ms after stimulus onset in the occipital cortex which cannot be attributed to the differences in the low-level physical features of the stimuli. We also found that early cortical responses are sensitive to the change of identity and emotional expression, and face inversion. Our studies suggested that an early stage of face processing takes place around 100 ms after stimulus onset. At later latencies we found differences in locations and dynamics of the identified sources for frequent (standard) and rare (target) faces which are likely to represent neuronal correlates of detection of a change in the visual stimulus.