Figure 8.

Dissection of the CR of a left hemisphere. (A) According to the previous description of the subinsular area (see Fig. 4), we opened and lifted, using two green pins, the EC layer within the anterior third, exposing the LN. Posterior to that location, we removed LN grey matter and identified the posterior limb of the IC. In this way, the anatomical layer-by-layer organisation of the basal ganglia region was clearly summarised. We proceeded in a caudal-to-cranial direction, exposing the fibres of the CR coming from the superior margin of the LN. Then, we removed the IFG cortex at the level of the middle and posterior third, isolating the SLF (blue tag a and b, pink arrow). We opened two windows along the SLF to expose the course of fibres directly through the CR to the pre-central (red arrow) and post-central (green arrow) cortices. The posterior limb of the CR is a crucial node for projective connectivity; it contains ascending fibres of the posterior thalamic radiation to the cortex, cortico-spinal fibres to the motor nuclei of the upper and lower extremity and trunk, as well as cortico-rubral and cortico-pontine fibres. (For a more detailed analysis of CR anatomy, see Chowdhury et al. 2010.) (B) Fibre tracking of the CR (blue fibres), and the indirect (green, yellow fibres) and direct (red fibres) components of the SLF. As demonstrated by our dissections, the perpendicular orientation of the vertical projective pre-central (red arrows) and post-central (green arrow) fibres with respect to the supero-inferior and antero-posterior oriented SLF (pink arrow) was clearly indicated. CS, central sulcus; EC, external capsule; IC, internal capsule; IFG, inferior frontal gyrus; LN, lenticular/lentiform nucleus; PreCG, pre-central gyrus; PostCG, post-central gyrus.