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Abstract

Multisensory interactions emerge in a distributed neural system encompassing primary sensory and higher-order association areas. Multiple functional brain architectures have been proposed to mediate multisensory interactions in low-level auditory regions including feedforward thalamocortical, direct connections between sensory areas and feedback from higher-order association areas such as IPS or STS. We will review the potential and limitations of combining functional imaging and effective connectivity analyses for characterizing functional architectures of multisensory integration. In a series of three audiovisual integration studies, we combined dynamic causal modeling and Bayesian Model comparison to arbitrate between neural models where crossmodal effects are mediated via ‘direct‘ V1-A1 connectivity, ‘indirect‘ feedback connectivity from STS or both mechanisms. The first study manipulated the presence/absence of auditory and visual inputs and demonstrated that low level audiovisual salience effects are mediated via both direct and indirect mechanisms of audiovisual integration. The second study showed that audiovisual synchrony effects in low-level sensory areas are mediated primarily via direct connectivity. The third study demonstrated that semantic audiovisual (in)congruency effects in higher order visual object areas are elicited by direct influences from auditory areas rather than top-down effects from prefrontal cortices. We conclude by critically reviewing interpretational ambiguities and pitfalls of Dynamic Causal Modelling results based on fMRI data in humans.