Audio–visual congruency alters power and coherence of oscillatory activity within and between cortical areas

• DOI: 10.1016/j.neuroimage.2013.04.064
• Publication Date: 2013-05-02T01:45:43Z
• Authors: Joachim Lange; Nadine Christian; Alfons Schnitzler
• Keywords: Male; 0301 basic medicine; Brain Mapping; Frontal Lobe; Young Adult; 03 medical and health sciences; 0302 clinical medicine; Biological Clocks; Speech Perception; Visual Perception; Humans; Female; Nerve Net; Visual Cortex

Dynamic communication between functionally specialized, but spatially distributed areas of the brain is essential for effective brain functioning. A candidate mechanism for effective neuronal communication is oscillatory neuronal synchronization. Here, we used magnetoencephalography (MEG) to study the role of oscillatory neuronal synchronization in audio-visual speech perception. Subjects viewed congruent audio-visual stimuli of a speaker articulating the vowels /a/ or /o/. In addition, we presented modified, incongruent versions in which visual and auditory signals mismatched. We identified a left hemispheric network for processing congruent audio-visual speech as well as network interaction between areas: low frequency (4-12 Hz) power was suppressed for congruent stimuli at auditory onset around auditory cortex, while power in the high gamma (120-140 Hz)-band was enhanced in the Broca's area around auditory offset. In addition, beta-power (20-30 Hz) was suppressed in supramarginal gyrus for incongruent stimuli. Interestingly, coherence analysis revealed a functional coupling between auditory cortex and Broca's area for congruent stimuli demonstrated by an increase of coherence. In contrast, coherence decreased for incongruent stimuli, suggesting a decoupling of auditory cortex and Broca's area. In addition, the increase of coherence was positively correlated with the increase of high gamma-power. The results demonstrate that oscillatory power in several frequency bands correlates with the processing of matching audio-visual speech on a large spatio-temporal scale. The findings provide evidence that coupling of neuronal groups can be mediated by coherence in the theta/alpha band and that low frequency coherence and high frequency power modulations are correlated in audio-visual speech perception.