Early cortical responses are sensitive to changes in face stimuli

Face-related processing has been demonstrated already in the early evoked response around 100 ms after stimulus. The aims of this study were to explore these early responses both at sensor and cortical source level and to explore to what extent they might be modulated by a change in face stimulus. Magnetoencephalographic (MEG) recordings, a visual oddball paradigm, and a semiautomated spatiotemporal source localization method were used to investigate cortical responses to changes in face stimuli. Upright and inverted faces were presented in an oddball paradigm with four conditions; standards and deviants differing in emotion or identity. The task in all conditions was silent counting of the target face with glasses. Deviant face stimuli elicited larger MEG responses at about 100 ms than standard ones did but only for upright faces. Spatiotemporal source localization up to 140 ms after stimulus revealed activation of parietal and temporal sources in addition to occipital ones, all of which demonstrated differences in locations and dynamics for standards, deviants, and targets. Peak latencies of the identified cortical sources were shorter for deviants than standards, again only for upright faces. Our results showed differences in cortical responses to standards and deviants that were more pronounced for upright than for inverted faces, suggesting early detection of face-related changes in visual stimulation. The observed effect provides new evidence for the face sensitivity of the early neuromagnetic response around 100 ms.