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 ∼ 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 ∼ 250 ms reflects the transient activation of object representations, with largest responses for upright faces, in the right hemisphere.