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The insular lobe reaches its greatest extent and morphologic differentiation in primates culminating in humans. It consists of four to six gyri that appear like a fan covered by the frontal, parietal, and temporal opercula. The human insula has three cytoarchitectonic subdivisions that are similar to those described for the rhesus macaque. Recent studies have addressed the myelo- and chemoarchitectonics of the primate insula. With the aid of a variety of methods investigators have demonstrated that the insular lobe has connections with: (1) portions of the frontal, parietal, and temporal lobes as well as of the cingulate gyrus, (2) the basal nuclei especially the tail of the caudate, putamen, and claustrum, (3) the amygdaloid body and other limbic constitutents, and (4) the dorsal thalamus. Experimental studies coupled with observations in humans provide the basis for a number of suggestions regarding the functional aspects of the insular lobe. The insula may play a role as a: (1) visceral sensory area, (2) visceral motor area, (3) supplementary motor area, (4) vestibular area, and (5) an area related to certain aspects of speech and/or language. While the broad concept of the insula has been outlined, the elucidation of its connections and functions remains to be completed by future researchers.
James R. Augustine (Fri,) studied this question.