Figure 5.

Tractography-based reconstructions of large association and projection tracts of the homuncular cortex. (A) Short association tracts connecting the precentral and postcentral gyri. In the hand knob region, these U-shaped tracts occupy a large volume and show a high degree of complexity (displayed in green, red and yellow colours). In the ventral region of the face and tongue (dark blue and cyan tracts) and dorsal region of the legs and toes (purple tracts) these connections are less prominent. (B) Short association (red) and long projection (green) tracts of the hand knob region from a lateral (upper left), dorsal (lower left) and posterior (right) view. The dashed line indicates the trajectory of the central sulcus. The short association tracts converge to the precentral regions of the hand knob area from the postcentral gyrus and the posterior regions of the superior and middle frontal gyri. The projection tracts are enclosed within the U-shaped tracts and connect the precentral gyrus to the putamen (corticostriatal fibres), the pontine nuclei (corticopontine tracts) and the spinal cord (corticospinal tract). (C) The fronto-insular tracts connect the frontal opercular cortex to the anterior insula. The connections from the precentral and subcentral/postcentral cortex are displayed in yellow and green, respectively. Please note that there is no correspondence between the colours used for these images and the colours in the previous figures. All images modified from Catani et al. (2012).