Cortico-Cortical Connectivity in the Human Brain: A Study on the Cortical White Matter

The human cortical white matter has a volume nearly as large as the grey matter. Most of it is composed of bers connecting the cortex to itself. These bres can be divided into the following systems: 1) short bres which follow the gyri and sulci of the grey matter (the U- bre-system), 2) longer bres which make short-cuts between more distant gyri, 3) long bres which run in fascicles in the depth of the white matter and connect the different cortical lobes with each other, and 4) bres of the Corpus callosum. In this study we make an estimate of the quantitative composition of some of these sytems. This gives insights into the organization of cortico-cortical connectivity in the human brain which is otherwise difcult to approach. In a rst approach, we dissected the long-range fascicles in the depth of the white matter. Measuring their cross sectional areas and multiplying these by the assumed density of bres one can estimate the number of bres in these fascicles. It turned out to be of the orders of and P.QSR P.Q