Figure 4.

In this series of pictures we performed a step-by-step dissection of the basal ganglia region of a left hemisphere, proceeding in a latero-medial direction. (A) After removal of the insular cortex, we considered three trapezoid-shaped regions within the subinsular area: anterior (red trapezoid); middle (yellow trapezoid); and posterior (blue trapezoid). (B) Within the anterior third, at the level of the limen insulae, we removed the grey matter of the cls and, on a deeper layer, exposed a thick WM stem corresponding to the point where two fascicles (i.e. UF and IFOF), which connect the frontal lobe to the other brain regions, converge (green-coloured WM area). (C) Within the middle third, we completely exposed the EC. More dorsally, we removed the posterior third of the frontal cortex and exposed the SLF fibres underneath the IFG (blue tag, black asterisk). (D) Within the posterior third, the EC was removed, exposing the grey matter of the LN (for a detailed analysis of the anatomy of the basal ganglia region, see Heimer, 2000 and Tamraz & Comair, 2006). In this panel, we also defined the posterior course of the IFOF (green arrow) from the limen insulae region (blue tag a) and of the SLF (blue tag b). (E) Finally, we exposed IC fibres, forming the CR, which take a vertical course (red arrow) at a deeper level than the horizontally oriented SLF (blue arrow; see also Fig. 8 and Chowdhury et al. 2010 for a more detailed analysis of IC connectivity). At the level of the limen insulae, we separated the IFOF (blue tag a), which runs from the frontal region to the posterior brain territories (green arrow), from the antero-ventral UF (yellow arrow), which connects the frontal and temporal poles. EC, external capsule; cls, claustrum; IC, internal capsule; IFG, inferior frontal gyrus; LN, lenticular/lentiform nucleus; UF, uncinate fascicle.