engleski

Early processing of a deviant in an oddball paradigm including upright and inverted faces: an EEG/MEG study.

Neuroimaging studies on face processing in humans reported face sensitive N170 ERP component and its magnetic counterpart M170. This component is larger and later for inverted faces than magnetic for upright faces. Face processing related activation was localized in fusiform gyri. The aim of our study was to investigate even earlier MEG and ERP responses to the upright and inverted facial stimuli in an oddball paradigm. Neurodynamic measurements were conducted at the BioMag laboratory using a 306-channel Vectorview system in the parallel with a 60-channel EEG. Eight male subjects with available MR scans participated in the study. Face stimuli were presented centrally in an oddball paradigm. Four combinations of standard and deviant stimuli were employed: 1) happy standard, neutral deviant ; 2) neutral standard, neutral deviant ; 3) inverted happy standard, inverted neutral deviant ; 4) inverted neutral standard, inverted neutral deviant. The task was silent counting of the second deviant (face with glasses). Spatio-temporal localization used multiple-current dipole model in a spherical volume conductor. Up to four sources were identified during the first 140 ms after stimulus onset in the occipital, occipito-temporal, and parietal regions. The temporal sequence and strength of current dipoles indicated significant individual variability. However, most subjects showed early differences in source locations for upright and inverted faces. Distinct dynamics and locations of current sources for the same neutral deviant face in four conditions indicated the existence of a sensory-memory trace for the standard to which the deviant was compared.

MEG (magnetoencephalography); face processing; spatio-temporal source localization

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