| Abstract No.: | B-D2160A |
| Country: | Canada |
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| Title: | MULTIMODAL INPUT IN MOUSE PRIMARY VISUAL CORTEX : AN ANATOMICAL STUDY |
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| Authors/Affiliations: | 1 Valérie Charbonneau*; 1 Marie-Eve Laramée; 1 Gilles Bronchti; 1 Denis Boire;
1 Université du Québec à Trois-Rivières, QC, Canada
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| Content: | Objectives: Until recently, primary sensory cortices were thought to be unimodal. But recent evidence suggests that direct connections exist between these primary cortices. In the macaque, direct projections from the primary auditory area (A1) to the primary visual cortex (V1) were shown (Falchier et al. 2002). Also, direct projections from A1 to early visual, olfactory, and somatosensory cortical areas were demonstrated in the Mongolian gerbil (Budinger 2000a). Several studies demonstrate activation of the primary visual cortex following diverse regimen of visual deprivations and following early blindness. Cross-modal activation of the visual cortex following blindness is believed to arise through three possible mechanisms:1 unmasking of already present cortical connections, 2 Sprouting of novel cortical connections and 3 enhancement of cortical intermodal connections. Studies in humans have demonstrated the onset of visual cortex activation following relatively short periods of blindfolding. This suggests that the primary visual cortex in normal sighted subjects receives afferents either from multisensory association cortices or primary sensory cortices dedicated to non-visual modalities. In this study, the cortical and subcortical afferents to the primary visual cortex were investigated in order to test the hypothesis that the visual cortex in normal subjects receives non-visual sensory input.
Materials and methods: The sensitive bi-directional tracer, B fragment of cholera toxin and biotinilated dextrans were injected in the primary visual cortex of C57BL6 sighted mice. Injection site in V1 covered all cortical layers. Retrogradely labelled cell bodies were charted using Neurolucida software and quantification of the laminar distribution of cells was performed using Neurolucida explorer software (MBF Bioscience).
Results: Results demonstrate direct projections to the visual cortex from primary auditory and primary somatosensory (S1) cortices as well as from known multisensory association cortices. Moreover, retrogradely labeled cell bodies in A1 and S1 were found both in supra- and infragranular layers but mostly in infragranular layers. This suggests a feedback-type influence of these areas onto V1.
Conclusion: This study provides evidence that information from different sensory modalities can be integrated at early cortical stages. This is in agreement with other studies showing that primary sensory cortices are not limited to purely unimodal processing and that visual cortex activations following visual deprivations can be explained partly by already present intermodal corticocortical connections. |
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