Brain responses to repetitions of human and animal faces, inverted faces, and objects: an MEG study.

Recent studies have identified a prominent face-selective ERP response to immediate repetitions of faces approximately 250 ms (N250r) which was strongly attenuated or eliminated for control stimuli (Schweinberger, Huddy, and Burton 2004, NeuroReport, 15, 1501-1505). In the present study we used a 148-channel whole head neuromagnetometer to investigate event-related magnetic fields (ERMFs) elicited by repetitions of exemplars of human faces, inverted human faces, primate faces, and car fronts. Participants counted rare pictures of butterflies interspersed in a series of pairs of one of these categories. The second stimulus of each pair could either be a repetition or a non-repetition of the first stimulus. We observed prominent M100 (90-140 ms) and M170 (140-220 ms) responses. Both M100 and M170 were insensitive to repetition and showed little differences between stimulus categories, except for a slight increase and delay of M170 to inverted faces. By contrast, we observed a repetition-sensitive M250r response (220-330 ms). This M250r was larger for upright human and primate faces when compared to both inverted human faces and cars, a finding that was specific for right hemispheric sensors. Source localization suggested different generators for M170 and M250r in occipitotemporal and fusiform areas, respectively. These findings suggest that repetition-sensitive brain activity approximately 250 ms reflects the transient activation of object representations, with largest responses for upright faces, in the right hemisphere.