Multi-modal multi-scale imaging reveals that long-association cortico-cortical systems are composed of short-range relay fibers

Motivation: Obtaining accurate anatomical information of connectional neuroanatomy across scales is crucial to improve in-vivodiffusion MRI techniques and advance our understanding of the brain white matter circuitries. Goal(s): To reveal the mesoscopic organization of the SLF-I, a major cortico-cortical fiber association system of the human brain. Approach: We combine multi-scale, multi-species, multi-modality connectional data from humans and macaques to investigate the structural connectivity of medial fronto-parietal cortical regions. Results: We provide preliminary novel evidence that the SLF-I is composed of a succession of shorter relay fibers, which, in lower-resolution dMRI tractography result erroneously in a long, direct association bundle. Impact: The mesoscopic anatomical validation of major white matter pathways in the human brain will increase the accuracy of their reconstruction in vivo, and open new avenues for our understanding of the functional substrates of these different connections.