The term dysgranular insula refers to a part of the insula defined on the basis of internal structure. It is classified as neocortex ( proisocortex component ). It forms a wide diagonal, caudoventral to rostrodorsal band across the center of the insula. It is bounded dorsally by the granular insula, from which it differs by lack of two distinct granular layers. And it is bounded ventrally by the agranular insula, from which it differs by the presence of granule cells grouped in a single layer or as distinct clusters ( Mesulam-1982 ). The density of granule cells follows a declining gradient from the border with the granular insula to the border with the agranular insula. The dysgranular insula differs from the dysgranular insular cortex (Roberts) by its much greater width. A study based on thicker histological sections than examined in the Roberts-1963 study revealed clusters of granule cells in the agranular insular cortex (Roberts) and led to incorporation of that area into the dysgranular insula ( Mesulam-1982 ). In the rat ( Swanson-2004 ) and the mouse ( Dong-2004 ) the dysgranular insula is identified with the gustatory cortex.