Insular Region. A, The opercular lips of the sylvian fissure have been removed to expose the insula. The central sulcus, the deepest insular sulcus, separates the insula into larger anterior and smaller posterior portions. The anterior portion consists of three short gyri (anterior, middle, and posterior) arranged in a radiating pattern that converges at the insular pole located at the anteroinferior edge of the short insular gyri. The anterior and posterior long gyri extend backward and upward from the limen insulae. The transverse insular gyrus is directed medially from the insular pole and is continuous with the posterior orbital gyri anteriorly. The inferior limiting sulcus is positioned below the long gyri of the insula and separates the insula from the sylvian surface of the temporal lobe. The superior limiting sulcus separates the insula from the sylvian surface of the frontal and parietal lobes. B, Lateral view of the insula in another specimen. The opercular lips of the sylvian fissure have been removed. The limen insulae is a slightly raised, arched ridge located at the junction of the sphenoidal and operculoinsular compartments of the sylvian fissure and extends from the temporal pole to the orbital surface of the frontal lobe. The insular pole is located at the anteroinferior edge of the insula, and the insular apex is the highest and most prominent laterally projecting area on the insular convexity. C, Removal of the cortical gray matter of the long and short insular gyri and extreme capsule, exposing the claustrum and external capsule. The claustrum has a dorsal (posterosuperior) part, composed of compact gray matter, and a ventral (anteroinferior)part, formed by islands of gray matter intermixed with and fragmented by fibers of the uncinate and inferior occipitofrontal fasciculi. The external capsule also has a ventral (anteroinferior) part composed of the fibers of the uncinate and inferior occipitofrontal fasciculi exposed under the cortex of the limen insulae, and a dorsal (posterosuperior) part formed by a group of radiating fibers, the claustrocortical fibers, which converge in and merge with the gray matter of the dorsal claustrum, forming a characteristic spoke-and-wheel pattern with its center at the dorsal claustrum. D, DTI-based tractogram showing the ventral and dorsal portions of the external capsule after selecting three ROIs, anterior (green), middle (orange), and posterior (blue), in the region of the insula between the insular cortex and putamen (inset in F). The ventral portion (green) is formed by the uncinate and inferior occipitofrontal fasciculi, and the dorsal portion has been divided in anterior and posterior parts. The anterior part of the dorsal portion (orange) is formed by multiple fibers coursing between the superior frontal, precentral, and postcentral gyri and the dorsal claustrum area just above the uncinate and occipitofrontal fasciculi. The posterior part of the dorsal portion (blue) is formed by several loops connecting the superior parietal lobule and parieto-occipital region to the dorsal claustrum. The dorsal external capsule contains the claustrocortical system, which has a topographical organization. E, Further step in the dissection of the claustrocortical fibers. Removal of the claustrocortical fibers of the dorsal external capsule peels away the gray matter of the dorsal claustrum. The fibers from the posterior part of the dorsal external capsule enter the posterior part of the dorsal claustrum, and the fibers coming from the anterior part enter the anterior part of the dorsal claustrum. The fibers of the ventral portion of the external capsule belong to the uncinate and inferior occipitofrontal fasciculi, which traverse the most anterior and inferior parts of the claustrum to create the gray matter islands forming the ventral claustrum. F, Tractographic reconstruction of the inferior occipitofrontal fasciculus, which is formed by a group of fibers coming from the prefrontal region and situated dorsal to the frontal fibers of the uncinate fasciculus. At the frontotemporal transition zone, the fasciculus narrows in section as it swings around the lower external side of the putamen and continues posteriorly toward the middle and posterior temporal region. It forms part of the ventral portion of the extreme and external capsule. (Images courtesy of E de Oliveira)