engleski

Face activated neurodynamic cortical networks

The purpose of our studies was to investigate dynamics of neuronal processes underlying face perception. We constructed a novel set of stimuli which allowed us to determine the earliest dissociation of cortical responses to faces and objects avoiding the differences in the low-level physical features of the stimuli. The oddball paradigm was employed to explore brain responses to changes in face stimuli. We used magnetoencephalography (MEG), electroencephalography (EEG) and multi-start spatio-temporal source analysis to estimate locations and sequence of activation of the brain regions involved in processing of face and non-face stimuli. We found evidence that early dissociation of face and object processing takes place around 100 ms after stimulus onset in the occipital cortex. Our data suggest that nonlinearity in the brain response is larger for face and object than for meaningless control stimuli. Multi-start spatio-temporal localization approach enabled identification of the multiple cortical regions involved in face processing during the first 140 ms after stimulus onset ; besides occipital sources, parietal and temporal sources were identified. We found an early effect of face inversion around 100 ms at the source level. Distinct source locations and dynamics for standards and deviants provided evidence for an early detection of change in facial stimuli. For some subjects we found very early onset of the activity in the fusiform face gyrus (FFG) which is in agreement with intracranial recordings. Target faces elicited activation of the frontal sources around 300 ms and subsequent parietal sources. The identified fronto-parietal network was selectively activated by the attentional switch to the target. Our results suggest that already around 100 ms face-related processing takes place. Locations and dynamics of the identified sources indicated a distributed cortical network involved in the face processing with a pronounced interindividual variability. Acknowledgments: Funded by the Croatian Ministry of Science, Education, and Sport (grant 199-1081870-1252) ; National Foundation for Science, Higher Education and Technological Development of the Republic of Croatia ; and the Centre for International Mobility, Finland.

magnetoencephalography (MEG); face processing; object recognition; human visual system; nonlinearity

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