Abstract
Multisensory integration is a process by which signals from different sensory modalities are combined to facilitate detection and localization of external events. One substrate for multisensory integration is the midbrain superior colliculus (SC) which plays an important role in orienting behavior. In rodent SC, visual and somatosensory (whisker) representations are in approximate registration, but whether and how these signals interact is unclear. We measured spiking activity in SC of anesthetized hooded rats, during presentation of visual- and whisker stimuli that were tested simultaneously or in isolation. Visual responses were found in all layers, but were primarily located in superficial layers. Whisker responsive sites were primarily found in intermediate layers. In single- and multi-unit recording sites, spiking activity was usually only sensitive to one modality, when stimuli were presented in isolation. By contrast, we observed robust and primarily suppressive interactions when stimuli were presented simultaneously to both modalities. We conclude that while visual and whisker representations in SC of rat are partially overlapping, there is limited excitatory convergence onto individual sites. Multimodal integration may instead rely on suppressive interactions between modalities.
Highlights
Multisensory integration is a process by which signals from different sensory modalities are combined to facilitate detection and localization of external events
We first characterize responses to visual and whisker stimuli presented in isolation, and ask how these responses are changed during simultaneous presentation
Activity at the 3 most superficial sites is not modulated by either whisker or visual stimulus, and these sites are likely to be located above superior colliculus (SC); deeper sites show primarily visual responses
Summary
Multisensory integration is a process by which signals from different sensory modalities are combined to facilitate detection and localization of external events. In single- and multi-unit recording sites, spiking activity was usually only sensitive to one modality, when stimuli were presented in isolation. We observed robust and primarily suppressive interactions when stimuli were presented simultaneously to both modalities. While a number of brain areas are likely to be involved in multisensory integration[4,5,6], the most studied is the superior colliculus (SC), an evolutionary ancient midbrain structure that receives inputs from multiple sensory modalities and helps orient subsequent behavior[7,8,9]. As in cat and primate, some of these neurons appear unisensory when stimuli are presented separately to each modality, and multisensory interactions may only become apparent during multisensory presentations[26]. We first establish the spatial and temporal overlap of visual and whisker inputs to SC, and show www.nature.com/scientificreports/
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