Combined diffusion-weighted and functional magnetic resonance imaging reveals a temporal-occipital network involved in auditory-visual object processing.

Anton L Beer,Tina Plank,Georg Meyer,Mark W Greenlee

doi:10.3389/fnint.2013.00005

Anton L Beer, Tina Plank + Show 2 more

Open Access

https://doi.org/10.3389/fnint.2013.00005

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Abstract

Functional magnetic resonance imaging (MRI) showed that the superior temporal and occipital cortex are involved in multisensory integration. Probabilistic fiber tracking based on diffusion-weighted MRI suggests that multisensory processing is supported by white matter connections between auditory cortex and the temporal and occipital lobe. Here, we present a combined functional MRI and probabilistic fiber tracking study that reveals multisensory processing mechanisms that remained undetected by either technique alone. Ten healthy participants passively observed visually presented lip or body movements, heard speech or body action sounds, or were exposed to a combination of both. Bimodal stimulation engaged a temporal-occipital brain network including the multisensory superior temporal sulcus (msSTS), the lateral superior temporal gyrus (lSTG), and the extrastriate body area (EBA). A region-of-interest (ROI) analysis showed multisensory interactions (e.g., subadditive responses to bimodal compared to unimodal stimuli) in the msSTS, the lSTG, and the EBA region. Moreover, sounds elicited responses in the medial occipital cortex. Probabilistic tracking revealed white matter tracts between the auditory cortex and the medial occipital cortex, the inferior occipital cortex (IOC), and the superior temporal sulcus (STS). However, STS terminations of auditory cortex tracts showed limited overlap with the msSTS region. Instead, msSTS was connected to primary sensory regions via intermediate nodes in the temporal and occipital cortex. Similarly, the lSTG and EBA regions showed limited direct white matter connections but instead were connected via intermediate nodes. Our results suggest that multisensory processing in the STS is mediated by separate brain areas that form a distinct network in the lateral temporal and inferior occipital cortex.

Highlights

Identifying objects or actions in our environment usually relies on multiple sources of sensory cues such as sounds and images
The activity map in the auditory cortex further extended to lateral parts of the superior temporal gyrus (STG), which likely correspond to lateral belt and parabelt regions of the auditory cortex
The contrast comparing responses to speech sounds with sounds generated by body movements (AS vs. AB) (Figure 2C) revealed a relatively distinct region in the lateral STG associated with phonological processing (Turkeltaub and Coslett, 2010; Woods et al, 2011)

Summary

Introduction

Identifying objects or actions in our environment usually relies on multiple sources of sensory cues such as sounds and images. (degraded) bimodal auditory-visual stimuli elicited larger BOLD responses in msSTS than predicted by the sum of the BOLD responses to corresponding unimodal stimuli (Calvert et al, 2000; Werner and Noppeney, 2010b). Such “superadditive” responses are not always observed (Hocking and Price, 2008; Meyer et al, 2011) and likely require degraded or noise stimuli (Laurienti et al, 2005; Angelaki et al, 2009). Other studies adopting salient (non-degraded) bimodal stimuli observed “subadditive” EEG/MEG responses (Schröger and Widmann, 1998) with a source in the STS (Raij et al, 2000; Cappe et al, 2010)

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