Spatial convergence of distant cortical regions during folding explains why arteries do not cross the Sylvian fissure
Alyssa Brisbin, Ezequiel Goldschmidt, Maximiliano Nuñez, Alan Bush, Robert Friedlander
Introduction: The folding process places cortical regions that are separated by a large distance along the cortical surface in close proximity in three-dimensional (Euclidean) space. Some regions have a much higher cortical surface distance (CSD) to Euclidean distance (ED) ratio than others.
Objective: Here we explore the hypothesis that the CSD determines regions of common irrigation, as this measure corresponds with the distance along the pre-folded brain, where the arterial vascular network starts forming.
Methods: We defined a convergence index that compares the ED to CSD and applied it to the cortical surface reconstruction of the MNI ICBM152 brain template, a co-registered average of 152 normal brain MRIs. We then compared cortical convergence to the irrigation pattern of the major sulci and fissures of the brain, by assessing whether they were or not crossed by arterial vessels in 20 fixed hemispheres.
Results: The regions of maximum 1% convergence were clustered around the Sylvian fissure, which is the only brain depression that concentrates high convergence values along its edges. Arterial crossings were almost universally present in every major sulci of the brain, with the exception of the Sylvian fissure.
Conclusions: Sulci of fissures with low convergence values do not define vascular territories. The Sylvian fissure, the depression with the highest convergence values, is the only depression that did not have vascular crossings. In the adult brain the CSD, rather than the ED, predicts the irrigation pattern of the vascular network. Cortical convergence explains why arteries do not cross the Sylvian fissure.