Thalamic influences on multisensory integration

Abstract

In everyday life our brain often receives information about events and objects in the real world via several sensory modalities, because natural objects often stimulate more than one sense. These different types of information are processed in our brain along different sensory-specific pathways but are finally integrated into a unified percept. During the last years studies provided compelling evidence that the neural basis of multisensory integration is not restricted to higher association areas of the cortex but can already occur at low-level stages of sensory cortical processing and even in subcortical structures. In this article we will review the potential role of several thalamic structures in multisensory interplay and discuss their extensive anatomical connections with sensory-specific and multisensory cortical structures. We conclude that sensory-specific thalamic structures may act as a crucial processing node of multisensory interplay in addition to their traditional role as sensory relaying structure.

Acknowledgments

This work was funded by Deutsche Forschungsgemeinschaft Grants DFG-SFB-TR31/TPA8 and TP13.

Figures and Tables

Figure 1 Illustration of fMRI BOLD (blood oxygen level dependent) responses in subject-specific visual and auditory thalamus (adapted from Noesselt et al.53). Top: Brain section depicts visual (LGB, blue) and auditory (MGB, red) thalamus for one illustrative individual subject (for more details see Noesselt et al.53). The bar graphs below of the brain sections depict the height of the fMRI-signal for the experimental conditions deduced from subject-specific ROIs (region of interest; see bar graphs, with grey bars for sound conditions and black for no-sound for the three visual stimuli: high intensity, low intensity, no visual target). An enhanced fMRI-signal was found when a sound was added to a lower-intensity visual target, but no significant change in response when the same sound was added to a higher-intensity visual target in accord with the behavioral findings.

Figure 2 Brain-behavior relations for coupling of thalamic structures with higher association cortices as a function of behavioral performance. Right: The scatter plot depicts the relation between the size of the behavioral interaction pattern (i.e., the difference in subject's visual detection hit rate for sound minus no-sound conditions being more pronounced for lower-than higher-intensity visual targets; along the y-axis) and the significant changes in LGB- and MGB-seeded (conjunction) interregional coupling-strength (PPI, along the x-axis) with the remote region STS (shown on the left side). This analysis highlights stronger coupling of both LGB and MGB with multisensory STS for subjects with higher behavior benefit than for those with lower behavioral benefit (adapted from Noesselt et al.53).