Multiple multi-sensory networks involve the claustrum

Recent reports propose a role for the claustrum in multi-sensory integration. Since afferent and efferent projections subdivide the claustrum into sensory specific regions, this poses the question of how this structure could participate in multi-sensory integration. In the rat, particular modality specific regions have been shown to overlap, while others remain aloof. Using retrograde tracers such as FluoroGold and Diamidino Yellow we visualize the connections of the rat claustrum with primary and higher sensory areas. This allows us to quantify the topographic arrangement of projections between these cortical areas and the claustrum with respect to the known sensory map within the claustrum. Our results not only confirm previous reports of arealization within the claustrum, but also suggest new routes of multi-sensory interaction involving this structure. Of interest is our observation of significant overlap between somatosensory and frontal claustral zones. Tracer injections made at subcortical loci too reveal connectivity to somatosensory zones. However, multi-sensory integration could also rely on the intrinsic connectivity between different sensory zones. In this regard, using calcium binding proteins as markers, we investigate the spatial arrangement of different cell populations and the relation of their dendritic trees with respect to the different sensory zones in the claustrum. The extrinsic and intrinsic connectivity of the claustrum reveals a complex network with the claustrum as a node between different cortical sensory and association areas and suggests a prominent role of this structure in combining and modulating sensory information