engleski

Early face sensitive processing in the occipital cortex: An MEG study

Numerous studies have demonstrated an important role of the fusiform face area of the inferior temporal cortex and superior lateral temporal areas in the face processing. Few recent EEG and MEG studies have shown that the early response occurring between 90 and 140 ms after stimulus onset showed face sensitivity. The aim of this study was to identify earliest face sensitive neuronal substrate using spatio-temporal source localization approach. Visually evoked responses from eight subjects were recorded with a 306-channel Vectorview system at the BioMag Laboratory. Upright and inverted grayscale face stimuli were centrally presented in an oddball paradigm. We used CSST-MRIVIEW software for spatio-temporal localization and Monte Carlo analysis to assess the effects of the measurement noise on source location estimates. Among multiple foci identified in all subjects during the first 140 ms, one or two of them were located in the occipital cortex. Latencies of the identified sources were longer for inverted than upright faces confirming previous reports on the face inversion effect. Deviant faces elicited earlier response than standards, but only for upright faces. However, source amplitudes did not differ for standards and deviants. Monte Carlo analysis of their source location estimates support hypothesis of an early specific deviance-related activity. Latency modification by the appearance of rare stimuli only in upright conditions indicates that early difference in the response to standards and deviants is not caused by the low-level physical features of the stimuli because they are the same in upright and inverted conditions, but rather implies an important role of the occipital cortex in the face processing, in agreement with our recent study (Susac et al., HBM 2008, in print) and some fMRI reports.

MEG; face processing; oddball paradigm; occiptal cortex; M100

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