Topographic separation of fornical fibers associated with the anterior and posterior hippocampus in the human brain: An MRI‐diffusion study

Abstract

Background and ObjectiveEvidence from rat and nonhuman primate studies indicates that axons comprising the fornix have a characteristic topographical organization: projections from the temporal/anterior hippocampus mainly occupy the lateral fornix, whereas the more medial fornix contains fibers from the septal/posterior hippocampus. The aim of this study was to investigate whether the same topographical organization exists in the human brain.MethodsUsing high angular resolution diffusion MRI‐based tractography at 3T, subdivisions of the fornix were reconstructed in 40 healthy adults by selecting fiber pathways from either the anterior or the posterior hippocampus.ResultsThe tract reconstructions revealed that anterior hippocampal fibers predominantly comprise the lateral body of the fornix, whereas posterior fibers make up the medial body of the fornix. Quantitative analyses support this medial:lateral distinction in humans, which matches the topographical organization of the fornix in other primates.ConclusionThis novel tractography protocol enables the separation of fornix fibers from anterior and posterior hippocampal regions in the human brain and, hence, provides a means by which to compare functions associated with different sets of connections along the longitudinal axis of the hippocampus.

Using diffusion MRI data acquired with ultra-high gradients to improve tractography in routine-quality data

“…The Fornix (FX). The FX was defined as streamlines surrounding the thalamus, directly adjacent to the medial half of its superior and posterior surfaces (Pascalau et al 2018) and connecting the hippocampal formation (specifically CA1, CA3, and fimbria) with the anterior thalamic nuclei, the mammillary bodies, the medial septal nucleus, and the basal forebrain (Poletti and Creswell 1977;Christiansen et al 2017). A first inclusion ROI was placed on the coronal plane, inferior to the body of the CC, to outline the fornix body.…”

Brain commissures and related pathologies

“…Свод и его составные элементы образуют главный эфферентный путь, соединяющий гиппокамп и гипоталамус со структурами, лежащими вне височной доли. При этом волокна от передних и задних отделов гиппокампа расположены в разных областях тела свода: волокна от передних отделов гиппокампа располагаются латерально, а те, что связывают задние части, -более медиально [45]. Наряду с гиппокампом, поясной извилиной, сосцевидными телами и энторинальной корой свод входит в состав нейронных це-пей Папеца (Papez circuit), которые отвечают за формирование и консолидацию памяти [46].…”

Quantitative magnetic resonance imaging for segmentation and white matter extraction of the hypothalamus

“…Nonetheless, one remaining drawback of available procedures for hypothalamic segmentation and volumetry is the reliable exclusion of cerebrospinal fluid (CSF), the fornix, and other white matter tracts. The fornix is a large white matter bundle passing from the hippocampus through the hypothalamus to the mammillary bodies (Christiansen et al, 2016). In more posterior parts of the hypothalamus, the fornix is fully surrounded by hypothalamic tissue, appearing more diffuse and weaker in contrast on T 1 w images, further complicating its reliable and complete extraction.…”