Structural Connections of Functionally Defined Human Insular Subdivisions

The organization of the human insular cortex has traditionally been considered as an anterior-posterior dichotomy, where anterior and posterior subdivisions have unique structural and functional connections. However, recent functional neuroimaging research proposes a tripartite organization where insular subdivisions have both unique and overlapping functional profiles. Studies examining unique profiles show that the dorsal anterior insula (dAI) has connections with frontal areas supporting higher-level cognitive processes, the ventral anterior insula (vAI) has connections with limbic areas supporting affective processes, and the posterior insula (PI) has connections with sensorimotor areas supporting interoceptive processes. Studies examining overlapping profiles demonstrate that all 3 subdivisions can also have similar functional profiles. The structural organization supporting a functional tripartite insula organization presenting with overlapping and unique connections is currently unknown. We used a large HARDI diffusion magnetic resonance imaging (MRI) dataset (n = 199) to demonstrate novel visualizations of insula white matter tracts supporting a tripartite structure-function insula organization. Overlapping connections of all 3 insula subdivisions consisted of association pathways (inferior fronto-occipital fasciculus, uncinate fasciculus, arcuate fasciculus) while unique connections included the corona radiata, subcortical-cortical tracts, and horizontal and u-shaped tracts. These results generally support a tripartite structure-function organization of the insular cortex, with subdivisions that exhibit both overlapping and unique connectivity profiles.