Circuitry and functional aspects of the insular lobe in primates including humans

The progress made in understanding the insula in the decade following an earlier review (Augustine, Neurol. Res., 7 (1985) 2-10) is examined in this review. In these ten years, connections have been described between the insula and the orbital cortex, frontal operculum, lateral premotor cortex, ventral granular cortex, and medial area 6 in the frontal lobe. Insular connections between the second somatosensory area and retroinsular area of the parietal lobe have been documented. The insula was found to connect with the temporal pole and the superior temporal sulcus of the temporal lobe. It has an abundance of local intrainsular connections and projections to subdivisions of the cingulate gyrus. The insula has connections with the lateral, lateral basal, central, cortical and medial amygdaloid nuclei. It also connects with nonamygdaloid areas such as the perirhinal cortex, entorhinal, and periamygdaloid cortex. The thalamic taste area, the parvicellular part of the ventral posteromedial nucleus, projects fibers to the ipsilateral insular-opercular cortex. In the past decade, confirmation has been given to the insula as a visceral sensory area, visceral motor area, motor association area, vestibular area, and language area. Recent studies have expanded the role of the insula as a somatosensory area, emphasizing its multifaceted, sensory role. The idea of the insula as limbic integration cortex has been affirmed and its role in Alzheimer's disease suggested.