The superior frontal longitudinal tract: a connection between the dorsal premotor and the dorsolateral prefrontal cortices

Mudathir Bakhit,Kiyoshi Saito,Kenichiro Iwami,Ryo Hiruta,Masazumi Fujii,Masayuki Yamada,Taku Sato

doi:10.1038/s41598-020-73001-7

Mudathir Bakhit, Kiyoshi Saito + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-73001-7

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Abstract

A few studies have identified the structural connection between the premotor area and the lateral prefrontal cortex (DLPFC) as the frontal longitudinal system (FLS). This study investigated the existence of a direct segment (none U-fibre) of the superior part of the FLS (sFLS), which connects the dorsal premotor cortex (PMd) and DLPFC and analysed its asymmetry and termination point patterns. A dataset of diffusion-weighted images from 48 subjects was used for generalised q-sampling imaging tractography. Additionally, a white-fibre dissection was conducted in two right hemispheres. An analysis of spatial location, termination points, laterality, and correlation with the subjects’ gender or handedness was performed. The sFLS was found to have a deeper longitudinal bundle directly connecting the PMd and DLPFC. The bundle is referred to hereafter as the superior frontal longitudinal tract (SFLT). The SFLT was reconstructed in 100% of right and 88% of left hemispheres. It exhibited variable patterns in different subjects in their posterior terminations. In addition, it was found to possess a complicated spatial relationship with the adjacent bundles. The SFLT was revealed successfully in two cadaveric right hemispheres, where the posterior terminations were found to originate in the PMd independent of the superior longitudinal fasciculus.

Highlights

A few studies have identified the structural connection between the premotor area and the lateral prefrontal cortex (DLPFC) as the frontal longitudinal system (FLS)
The superior frontal longitudinal tract (SFLT) can be distinguished from the superficial U-fibres of the superior part of the FLS (sFLS)
The current work extensively studied the anatomy of the SFLT using generalised q-sampling imaging (GQI) tractography with a limited white fibre dissection, which focused on the anatomical terminations’ subcomponents and their asymmetry; this aspect, in particular, received little attention in previous reports[4,5,6]

Summary

Introduction

A few studies have identified the structural connection between the premotor area and the lateral prefrontal cortex (DLPFC) as the frontal longitudinal system (FLS). Using probabilistic tractography in humans, Tomassini et al identified a dorsal and ventral subregion of the premotor cortex (PMd and PMv) They revealed higher probabilities of connection for the PMd compared with the ventral subregion in both hemispheres for the cingulate gyrus, cingulate sulcus, and superior parietal lobule. Schulz et al studied the structural connectivity of prefrontal-premotor and prefrontal-motor connections using probabilistic tractography in a group of healthy aged participants and well-recovered chronic stroke patients They were able to reconstruct probable trajectories connecting the DLPFC with the premotor (dorsal and ventral). The same authors claimed that the FLS represents an extension of the superior longitudinal fasciculus (SLF) connecting fronto-parietal regions

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