Functional organization of the insula and inner perisylvian regions.

In the last few years, the insula has been the focus of many brain-imaging studies, mostly devoted to clarify its role in emotions and social communication. Physiological data, however, on which one may ground these correlative findings are almost totally lacking. Here, we investigated the functional properties of the insular cortex in behaving monkeys using intracortical microstimulation. Behavioral responses and heart rate changes were recorded. The results showed that the insula is functionally formed by two main subdivisions: (i) a sensorimotor field occupying the caudal-dorsal portion of the insula and appearing as an extension of the parietal lobe; and (ii) a mosaic of orofacial motor programs located in the anterior and centroventral insula sector. These programs show a progressive shift from dorsally located nonemotional motor programs (ingestive activity) to ventral ones laden with emotional and communicative content. The relationship between ingestive and other behaviors is discussed in an evolutionary perspective.