Involvement of top-down networks in the perception of facial emotions: a magnetoencephalographic investigation.

Conscious perception of the emotional valence of faces has been proposed to involve top-down and bottom-up information processing. Yet, the underlying neuronal mechanisms of these two processes and the implementation of their cooperation is still unclear. We hypothesized that the key substrates enabling conscious perception are differential participation of top-down and bottom-up networks. Using a visual-backward-masking paradigm, we assessed the participation of bottom-up and top-down networks in 12 healthy individuals by means of magnetoencephalography (MEG). Providing visual stimulation near the perceptual threshold enabled us to compare correctly and incorrectly recognized facial emotions and assess thereby differences in top-down and bottom-up modulation of the visual information processing using coherence analysis. For correctly recognized facial emotions, we found a right-hemispheric fronto-parietal network oscillating in the high-beta and low-gamma band and exerting top-down control as determined by the causality measure of phase slope index (PSI). In contrast, incorrect recognition was associated with enhanced coupling in the gamma band between left frontal and right parietal regions. Our results indicate that the perception of emotional face stimuli relies on the right-hemispheric dominance of synchronized fronto-parietal gamma-band activity.