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The degree of folding of a brain is traditionally estimated
by comparing the area of the cortical surface with the area
of its external surface, or the ratio between the pial
contour and the outer contour in successive coronal
sections. The Surface Ratio extends these ideas to obtain a
local estimate of the degree of cortical folding. For every
point x on the cortical surface we compute the cortical
area contained in a small sphere of fixed radius r centred
at x. If the brain were lissencephalic, the area inside the
sphere would be approximately that of the sphere's disc. We
estimated the local degree of folding through the surface
ratio:
![]() Reference Toro R et al (2008) Brain size and folding of the human brain. Cerebral Cortex |