Basal Ganglia Region. A, The dorsal external capsule and claustrum have been removed to expose the lateral surface of the putamen. The uncinate fasciculus, exposed by removing the cortical gray matter of the limen insulae, interconnects, in its most lateral portion, the orbitofrontal region with the temporal pole. Several island-like gray matter masses of the ventral claustrum are intermingled with the fibers of the uncinate fasciculus. The corona radiata spreads out around the putamen. B, Tractographic reconstruction of the uncinate fasciculus, analogous to the fiber dissection shown in A. Some radiating fibers of the dorsal external capsule are also displayed in continuity with vertical fibers of the superior longitudinal fasciculus (yellow arrow). This represents an artifact of the tractographic technique. When the voxel-averaged estimate of orientation cannot summarize the orientation of the underlying fibers, the tractography introduces continuity between the fibers where there is none. An accurate knowledge of the anatomy of the fiber systems acquired by means of the fiber dissection technique aids in the interpretation of the tractographic results. C, The putamen and globus pallidus have been removed to expose the internal capsule and anterior commissure. The internal capsule is continuous with the corona radiata, located deep to the superior longitudinal fasciculus. A characteristic white matter prominence is created by the intersection of the fibers of the corpus callosum and the corona radiata (red arrow). The lower part of the vertical and arcuate segments of the superior longitudinal fasciculus have been removed to expose the sagittal stratum, which contains the optic radiations and is the equivalent of the internal capsule at the posterior part of the hemispheres. The medial fibers of the uncinate fasciculus interconnect the frontomesial (gyrus rectus, subcallosal area) and the temporomesial (amygdala, anterior parahippocampal gyrus) regions. D, Tractographic reconstruction of the internal capsule and sagittal stratum. The internal capsule (orange and light and dark red) is in continuity with the corona radiata, which radiates toward the cortical hemispheric surface. The sagittal stratum (purple) is formed by the optic radiations and the parietopontine and occipitopontine fibers. E, Enlarged view of the internal capsule. The anterior limb of the internal capsule has an oblique anteroposterior orientation, and is composed of a group of fibers exiting and entering the anterior frontal region (orbitofrontal, prefrontal area). The intercapsular gray matter between the lenticular and caudate nucleus is intermingled with the fibers of the anterior limb to give it a dark appearance. The fibers of the anterior limb are positioned medially to the fibers of the posterior limb at the lower level of the internal capsule. The genu of the internal capsule has a craniocaudal orientation, is positioned lateral to the lower part of the anterior limb, and is formed by fibers from the prefrontal and precentral region. The posterior limb of the internal capsule is formed by fibers from the precentral and postcentral region, and has a slightly oblique posteroanterior direction. The retrolenticular portion of the internal capsule is composed of fibers coming from the posterior parietal (precuneus) and occipital (cuneus) cortex, and is oriented in a sagittal plane in their passage toward the internal capsule. The anterior commissure, which follows a mediolateral and slightly anteroposterior trajectory, is exposed at the anterior and basal pole of the globus pallidus. The substantia innominata (or basal forebrain) is a mass of gray matter located in front and beneath the anterior commissure, and above the anterior perforated substance. The medial fibers of the uncinate fasciculus are intermingled with islands of gray matter belonging to the ventral claustrum. F, Tractographic reconstruction of the internal capsule and anterior commissure. The anterior limb of the internal capsule (orange) is composed of frontopontine and thalamofrontal (anterior thalamic peduncle) fibers. The genu of the internal capsule (light red) contains fibers connecting the precentral cortex with the motor nuclei of the cranial nerves and the most anterior fibers of the superior thalamic peduncle (thalamo-precentral fibers). The posterior limb of the internal capsule (dark red) is formed by corticospinal, thalamo-postcentral (superior thalamic peduncle), corticopontine, and corticotegmental fibers. As in the fiber dissections, the anterior limb is situated medial to the genu, and the posterior limb lateral to the genu. Tractography allows observation of the fibers of the corona radiata, internal capsule, cerebral peduncle, and middle cerebellar peduncle at the same time. The anterior commissure (white) bifurcates in an anterior limb directed toward the temporal pole and a posterior limb that enters the sagittal stratum, and is directed toward the posterior temporal and occipital regions. G, Color-coded DTI map showing the ROIs selected for the reconstruction of the anterior commissure (white) in D and F and the uncinate fasciculus (orange) in B. H, Color-coded DTI map showing the ROIs selected for the reconstruction of the anterior limb (orange), genu (light red), posterior limb (dark red), and retrolenticular portion (purple) of the internal capsule displayed in D and F. (Images courtesy of E de Oliveira)