Magnetoencephalography Source Connectivity Pipeline Reveals Long-Range Connectivity in Audio-Visual Integration

We present a pipeline for analysing source-level brain connectivity, applied to data from an MEG study investigating audio-visual integration. The study involved both auditory and visual stimuli (Chinese spoken syllables and written characters) presented simultaneously to native Chinese speakers and a control group unfamiliar with the language. To identify significant differences in brain connectivity between the groups, source-level connectivity was examined using cluster permutation statistical analysis. For an improved source model in the absence of individual anatomy, the coregistration of MEG data with a template brain was enhanced using the fitted locations of primary auditory and visual responses. Connectivity results indicate that long-range connectivity in the Delta frequency band plays a crucial role in audio-visual integration. Specifically, native speakers showed Delta band connectivity following pathways between prefrontal and occipital sources bilaterally, with a left-hemisphere bias, and interhemispheric connections. Key regions engaged in this connectivity included the ventrolateral prefrontal cortex, anterior superior temporal gyrus, Heschl's gyrus, middle temporal area, occipital cortex (bilaterally) and fusiform face area. Connectivity patterns in other frequency bands were similar across both groups, or differences did not reach statistical significance. Interaction effect analysis further revealed group differences in the processing of congruent versus incongruent stimuli, with the fusiform face area showing differential engagement, though these effects generally trended below significance across regions. Significance: The presented pipeline enabled a detailed analysis of source-level connectivity in audiovisual integration. Our findings provide source-localized evidence that audiovisual integration is hierarchically organized by neural oscillations and shaped by language expertise.