Q-ball of inferior fronto-occipital fasciculus and beyond.

Eduardo Caverzasi,Nico Papinutto,Bagrat Amirbekian,Mitchel S Berger,Roland G Henry,Gaolang Gong

doi:10.1371/journal.pone.0100274

Abstract

The inferior fronto-occipital fasciculus (IFOF) is historically described as the longest associative bundle in the human brain and it connects various parts of the occipital cortex, temporo-basal area and the superior parietal lobule to the frontal lobe through the external/extreme capsule complex. The exact functional role and the detailed anatomical definition of the IFOF are still under debate within the scientific community. In this study we present a fiber tracking dissection of the right and left IFOF by using a q-ball residual-bootstrap reconstruction of High-Angular Resolution Diffusion Imaging (HARDI) data sets in 20 healthy subjects. By defining a single seed region of interest on the coronal fractional anisotropy (FA) color map of each subject, we investigated all the pathways connecting the parietal, occipital and posterior temporal cortices to the frontal lobe through the external/extreme capsule. In line with recent post-mortem dissection studies we found more extended anterior-posterior association connections than the “classical” fronto-occipital representation of the IFOF. In particular the pathways we evidenced showed: a) diffuse projections in the frontal lobe, b) fronto-parietal lobes connections trough the external capsule in almost all the subjects and c) widespread connections in the posterior regions. Our study represents the first consistent in vivo demonstration across a large group of individuals of these novel anterior and posterior terminations of the IFOF detailed described only by post-mortem anatomical dissection. Furthermore our work establishes the feasibility of consistent in vivo mapping of this architecture with independent in vivo methodologies. In conclusion q-ball tractography dissection supports a more complex definition of IFOF, which includes several subcomponents likely underlying specific function.

Highlights

Human cognition is supported by large-scale cortical and subcortical networks subserved by bundles of axons, connecting cortical and subcortical neurons
Streamline density maps were computed in the subjects’ native space and thresholded to obtain binary masks containing all voxels that were visited by at least one streamline in the residual bootstrap tractography. These masks were spatially normalized to the MNI space using the linear and non-linear transformations computed for the co-registration of the fractional anisotropy (FA) maps to the FMRIB Software Library (FSL) MNI
By combining q-ball tractography and Freesurfer parcellation we provided on a large group of individuals a consistent demonstration of Sarubbo et al post mortem findings [15], by using a similar description of the different subcomponents of the inferior fronto-occipital fasciculus (IFOF) (Fig. 6)

Summary

Introduction

Human cognition is supported by large-scale cortical and subcortical networks subserved by bundles of axons, connecting cortical and subcortical neurons. White matter fibers are usually classified as commissural (between hemispheres), projection (between higher and lower brain and spinal cord centers) or association fibers (between cortical regions within the same hemisphere). The latter are subdivided into short and long association fibers. The inferior fronto-occipital fasciculus (IFOF) is the longest associative bundle and it connects various parts of the occipital cortex, temporo-basal area and the superior parietal lobule to the frontal lobe [1]. After more than a century from its first descriptions (by Dejerine in 1895 and Curran in 1909) [8], the detailed anatomical definition of the IFOF is still under discussion within the scientific community; is it a distinct pathway or is it just a portion of a bigger bundle that includes the inferior longitudinal fasciculus (ILF) as well?

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