title: Audio-visual congruency alters power and coherence of oscillatory activity within and between cortical areas.
abstract: 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.
authors: Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Universitätsstraße 1, 40225 Düsseldorf, Germany. joachim.lange@med.uni-duesseldorf.de
authors: Joachim
authors: J
authors: Lange
authors: Nadine
authors: N
authors: Christian
authors: Alfons
authors: A
authors: Schnitzler
mesh_terms: D001683:Biological Clocks / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D013067:Speech Perception / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult