Neuronal architecture of the mouse insular cortex underlying its diverse functions

The insular cortex integrates interoceptive and exteroceptive information to mediate bodily homeostasis, emotion, learning, and potentially consciousness. However, the cellular and circuit substrates governing the insula and other associative cortices are poorly understood compared to primary cortices. Here, we quantify the dendritic morphology together with electrical properties, local inputs, and/or projections of 1,093 insular pyramidal neurons. These neurons are mapped onto a quantitative anatomical model of the insula based on a Nissl-staining coordinate framework. Using improved algorithms, we define 21 morphological, 12 electrical, and 9 input neuronal types, and identify several morphological and input types that are unique to the insula. Further, we find that morphological properties constrain and often predict inputs, electrical properties, or projection targets. Several morphological types are differentially distributed between the functionally distinct anterior and posterior insula, providing the substrates for a quantitative demarcation between the anterior and posterior insular subregions. Surprisingly, certain neuronal types receive intra-insular inputs originating far beyond canonical cortical columns. Functionally, these connections bridge a long-range thalamus-to-amygdalar circuit that potentially links sensory information to valence. Our work establishes a structure-and-function foundation for investigating the insular cortex.