Functional anatomy of the insula: new insights from imaging

Little is known about the functional anatomy of the insula. Several experimental data suggest that the organization of the insular connections from the different insular cytoarchitectonic regions is related to different functional domains within the insula, and recent electrophysiological and neuroimaging studies have shown the existence of an anterior-posterior organization within the insular cortex. To further investigate this point, we carried out a positron emission tomography (PET) study using fluorodeoxyglucose (F-18-FDG) in patients with medial temporal lobe epilepsy who experienced emotional or visceral symptoms that are supposed to be elicited in the insula. The aim of our study was to assess the existence of a functional insular somatotopic organization. FDG-PET studies were carried out in 18 epileptic patients. Data were analyzed using statistical parametric mapping (SPM96). The results showed that the emotional symptoms were correlated with hypometabolism in the anterior part of the ipsilateral insular cortex, while visceral symptoms were correlated with hypometabolism in the posterior part (p=0.001). This neuroimaging study demonstrates that the anterior part of the insular cortex corresponding to the agranular cortex subserves emotional functions while the posterior part of the insular cortex corresponding to the granular cortex subserves ascending visceral symptoms.