Figure 1.

Illustration of the convoluted cortical surface consisting of protrusions called gyri separated by troughs called sulci. Concave sulcal fundi and convex gyral crowns are connected by relatively straight sulcal walls. Axons from the other parts of the brain have to follow the shape of the gyral white matter to reach the gyral crown and sulcal walls (e.g. blue lines). This suggests that a gyral coordinate system based on the shape of the gyri might be predictive of fibre orientation in gyral white matter.