Spatiotemporal dynamics and connectivity pattern differences between centrally and peripherally presented faces.

Most neuroimaging studies on face processing used centrally presented images with a relatively large visual field. Images presented in this way activate widespread striate and extrastriate areas and make it difficult to study spatiotemporal dynamics and connectivity pattern differences from various parts of the visual field. Here we studied magnetoencephalographic responses in humans to centrally and peripherally presented faces for testing the hypothesis that processing of visual stimuli with facial expressions of emotions depends on where the stimuli are presented in the visual field. Using our tomographic and statistical parametric mapping analyses, we identified occipitotemporal areas activated by face stimuli more than by control conditions. V1/V2 activity was significantly stronger for lower than central and upper visual field presentation. Fusiform activity, however, was significantly stronger for central than for peripheral presentation. Both the V1/V2 and fusiform areas activated earlier for peripheral than for central presentation. Fast responses in the fusiform were found at 70-80 ms after image onset, as well as a response at 130-160 ms. For peripheral presentation, contralateral V1/V2 and fusiform activated earlier (10 ms and 23 ms, respectively) and significantly stronger than their ipsilateral counterparts. Mutual information analysis further showed linked activity from bilateral V1/V2 to fusiform for central presentation and from contralateral V1/V2 to fusiform for lower visual field presentation. In the upper visual field, the linkage was from fusiform to V1/V2. Our results showed that face stimuli are processed predominantly in the hemisphere contralateral to the stimulation and demonstrated for the first time early fusiform activation leading V1/V2 activation for upper visual field stimulation.