On the geometry of somatosensory representations in the Cortex

The processing of somatosensory information in the cortex is often described using body maps, where adjacent cortical regions correspond to adjacent body parts. Additionally, the somatosensory cortex follows a hierarchical structure, which extends from the primary somatosensory cortex (S1) to higher cortical regions. While previous studies have identified multiple body maps and various hierarchy relations, the large-scale organization of these maps and their interactions have been less explored. Using functional MRI with full-body light touch stimulation, we discovered that in S1, body and hierarchy maps are orthogonal, but this orthogonality does not extend to other regions. On a larger scale, both body representation and hierarchy exhibit a radial organization, with a few central extrema governing numerous cortical regions. Similar patterns of radial organization in the visual and auditory systems suggest that radial topography may be a general organizational feature across sensory systems.