Abstract
Behavioural performance requires a coherent perception of environmental features that address multiple senses. These diverse sensory inputs are integrated in primary sensory cortices, yet it is still largely unknown whether their convergence occurs even earlier along the sensory tract. Here we investigate the role of putatively modality-specific first-order (FO) thalamic nuclei (ventral posteromedial nucleus (VPM), dorsal lateral geniculate nucleus (dLGN)) and their interactions with primary sensory cortices (S1, V1) for multisensory integration in pigmented rats in vivo. We show that bimodal stimulation (i.e. simultaneous light flash and whisker deflection) enhances sensory evoked activity in VPM, but not dLGN. Moreover, cross-modal stimuli reset the phase of thalamic network oscillations and strengthen the coupling efficiency between VPM and S1, but not between dLGN and V1. Finally, the information flow from VPM to S1 is enhanced. Thus, FO tactile, but not visual, thalamus processes and relays sensory inputs from multiple senses, revealing a functional difference between sensory thalamic nuclei during multisensory integration.
Highlights
IntroductionThe bottom-up subcortical contribution to integrative processing is supported by the visual modulation of auditory thalamic responses in medial geniculate body (MGB)[19] and the convergence of visual and tactile responses in the VPM20
Behavioural performance requires a coherent perception of environmental features that address multiple senses
The present study aims to elucidate whether FO thalamic nuclei, which have been identified as major relay stations between the periphery and cortex, are involved in visual-tactile processing
Summary
The bottom-up subcortical contribution to integrative processing is supported by the visual modulation of auditory thalamic responses in medial geniculate body (MGB)[19] and the convergence of visual and tactile responses in the VPM20 Both FO thalamic nuclei send direct subcortical information to the cortex, in contrast to higher-order (HO) thalamic nuclei that provide a trans-thalamic relay from one part of the cortex to another[21]. We aim at elucidating the contribution of FO thalamic nuclei to the processing of visual-tactile information To this end, we combine simultaneous multi-site extracellular recordings from S1 and V1 as well as from VPM and dLGN with retrograde tracing of axonal connectivity within thalamo-thalamic and thalamo-cortical circuits of pigmented Brown Norway rats. In contrast to dLGN, cross-modal inputs consistently and significantly modulate network oscillations and neuronal firing patterns in VPM
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