Topography of distance-modulated multisensory object location encoding in mouse area RL

For animals to interact coherently with the external world, their brains must integrate object location information across sensory modalities, an inherently complex process. Each sensory modality samples distinct regions of external space, with object location encoded in fundamentally different reference frames: for example, visual representation of space begins with retinotopic maps, and tactile representation of space in the rodent whisker system starts with somatotopic maps.^1,2,3,4,5,6 To form an integrated representation of objects in space, the brain must reconcile differences in spatial coverage and reference frames. The posterior parietal cortex (PPC) has emerged as a key neural substrate for multimodal integration in mammals.⁷ Within mouse PPC, rostrolateral area (RL), located between primary visual and barrel cortex, serves as a hub for visuo-tactile integration in both supralinear and sublinear ways.^{8,9,10,11,12,13} A recent study has shown that RL neurons are tuned to binocular disparities, with a preference for very close objects, likely within whisker reach.¹⁴ Further, the coherent visual and tactile representation of upper and lower space in RL described recently implies the possible emergence of a unified multimodal framework for near space.¹¹ However, whether this reflects a true three-dimensional near-space representation or simply the aligned arrangement of retinotopic and somatotopic maps remains unresolved. Here, using high-resolution multimodal receptive field mapping in awake mice, we reveal a primarily co-aligned egocentric reference framework across modalities, which is also reflected in cortical topographical maps. We show that visuo-tactile integration is profoundly distance-dependent, affecting not only modality preference but also the mechanisms and linearity of integration.