Anatomo-functional organization of insular networks: From sensory integration to behavioral control

Classically, the insula is considered an associative multisensory cortex where emotional awareness emerges through the integration of interoceptive and exteroceptive information, along with autonomic regulation. However, since early intracortical microstimulation (ICMS) studies, the insular cortex has also been conceived as a mosaic of anatomo-functional sectors processing various types of sensory information to generate specific overt behaviors. Based on this, the insula has been subdivided into distinct functional fields: an anterior field associated with oroalimentary behaviors, a middle field involved dorsally in hand movements and ventrally in emotional reactions, and a posterior field engaged in axial and proximal movements. Nevertheless, the anatomo-functional networks through which these fields produce motor behaviors remain largely unknown. To fill this gap in the present study, we investigated the connectivity of the macaque insula using a multimodal approach which combines resting-state fMRI with data from tract-tracing injections in insular functional fields defined by ICMS, as well as in brain areas known to be connected to the insula and characterized by specific somatotopic organization. The results revealed that each insular functional field takes part in distinct somatotopically organized network modulating specific motor or visceromotor behaviors, extending previous models that subdivide the insula primarily based on the types of interoceptive and exteroceptive information it receives. Our findings posit the various insular sectors as interfaces that synthesize diverse interoceptive and exteroceptive inputs into coherent subjective experiences and decision-making processes, within an embodied and enactive framework, that moves beyond the traditional dichotomy between sensory experience and motor behavior.