Dorsal fronto-parietal connections of the human brain: a fiber dissection study of their composition and anatomical relationships.

The goal of this study was to detail the composition of dorsal fronto-parietal connections in the human brain, focusing on the dorsal component of superior longitudinal fasciculus (SLF), short association fibers, their three-dimensional organization, and relationships with adjacent projection and commissural fibers. Ten human cerebral hemispheres (five left and five right) were obtained from necropsy specimens. The technique for specimen preparation was adapted from that previously described by Ludwig and Klingler for spreading groups of white matter fibers, rendering tracts visible and dissectible. Near the superior border of the hemisphere, we observed an overall organization consisting of a succession of "U" fibers in both sides of a narrow and irregular intermediary layer of white matter. Dissection of the core fibers leads to the corona radiata (intermingled with the callosal radiations) on the lateral aspect and to the callosal radiations at the medial aspect of the hemisphere. Based on our findings, the fiber dissection technique does not provide evidence of the presence of long horizontal association fibers in such location, as suggested by brain imaging techniques. The results of this study lead us to hypothesize that dorsal regions of the frontal and parietal lobes superior to the level of the cingulate sulcus are connected by a succession of short association pathways. Dissectible long association fibers are only encountered in a zone restricted to a lower and deeper portion of the superior parietal lobule. These fibers are clearly integrated in the lower portions of the SLF/arcuate fasciculus complex.