Inter-individual variations and hemispheric asymmetries in structural connectivity patterns of the inferior fronto-occipital fascicle: a diffusion tensor imaging tractography study.

Abstract

Precise knowledge of the structural connectivity of white matter fascicles could yield new insights into function and is important for neurosurgical planning. Therefore, we aimed to provide a detailed map of the cortical terminations of the inferior fronto-occipital fascicle (IFOF), with special emphasis on putative inter-individual variations and hemispheric asymmetries. Deterministic diffusion tensor imaging-based tractography was used to perform virtual dissection of the IFOF in 20 healthy subjects. The IFOF was probed from a single seed region of interest placed within the external/extreme capsule, i.e. the white matter region of "obligatory passage" along the known path of the IFOF. This enabled to reconstruct all the fibers belonging to the IFOF and to provide the complete map of their cortical terminations. We observed widespread projections over a total of 11 cortical territories within the occipital, parietal, temporal and frontal lobes. Importantly, compared to previous studies we consistently found some inter-individual variability with several distinct patterns connecting subsets of the 11 cortical territories, and tangible differences between the two hemispheres. IFOF terminations within the superior parietal lobule were rightward lateralized, whereas terminations within the inferior frontal gyrus were leftward lateralized. Our results provide a clinically relevant map of IFOF's cortical terminations, including intra- and inter-individual variations. Right-left differences in connectivity patterns might be related to known functional asymmetries in the human brain, and reinforce the general evidence that the IFOF likely supports distinct clinical features and functional roles according to the (affected) hemisphere, such as language and spatial attention.