Cited by 189Advanced Neuroimaging Techniques and ApplicationsClassical Anatomy and HistologyFunctional Brain Connectivity Studies

The DOI matches its Crossref record; 82 of the 82 references it cites were found in a registry or an index; 22 of the 62 sources its claims cite were checked for support.

Superior Longitudinal Fasciculus: A Review of the Anatomical Descriptions With Functional Correlates

Open access
Janelle, Felix, Iorio-Morin, Christian, D'amour, Sabrina, Fortin, David·2022·Frontiers in Neurology

Abstract

The superior longitudinal fasciculus (SLF) is part of the longitudinal association fiber system, which lays connections between the frontal lobe and other areas of the ipsilateral hemisphere. As a dominant association fiber bundle, it should correspond to a well-defined structure with a clear anatomical definition. However, this is not the case, and a lot of confusion and overlap surrounds this entity. In this review/opinion study, we survey relevant current literature on the topic and try to clarify the definition of SLF in each hemisphere. After a comparison of postmortem dissections and data obtained from diffusion MRI studies, we discuss the specifics of this bundle regarding its anatomical landmarks, differences in lateralization, as well as individual variability. We also discuss the confusion regarding the arcuate fasciculus in relation to the SLF. Finally, we recommend a nomenclature based on the findings exposed in this review and finalize with a discussion on relevant functional correlates of the structure.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This review/opinion argues that the superior longitudinal fasciculus (SLF) remains anatomically and nomenclaturally controversial, despite being a major association fiber system. It recommends distinguishing the SLF from the arcuate fasciculus, questioning SLF I as separate from the cingulum, and recognizing asymmetric SLF II/III functional roles.

Key findings

  • The SLF is best defined as a fronto-parietal tract, whereas the arcuate fasciculus (AF) is a fronto-temporal tract; classifications that include the AF as part of the SLF are described as misleading.
  • SLF I, connecting parietal precuneus to superior frontal gyrus, appears assimilable to the cingulum, so its existence and role are unclear; SLF II and SLF III are described as distinct and asymmetric, with left-sided SLF II/III implicated in speech processing and right-sided SLF II/III in visuospatial functioning.
  • Wang et al.’s combined dMRI (\(n=10\)) and dissection (\(n=5\)) study found SLF II represented about 66% of total SLF volume and SLF III about 33%; left SLF II connectivity was linked to motor planning of language and/or syntax, right SLF II to attention regulation in spatial orientation.
  • The review highlights dMRI validation problems: 63–90% of white matter volume is estimated to contain crossing fibers, and in an international tractography competition most tractograms contained more invalid than valid bundles.

Methods

  • Narrative review/opinion based on a literature survey of SLF anatomy, nomenclature, lateralization, individual variability, AF relationship, and functional correlates.
  • The authors compare postmortem dissection and diffusion MRI/tractography studies and summarize studies reporting 2, 3, 3 plus AF, and 5 SLF divisions in a table.
  • No original cohort is analyzed; illustrative figures use open-source MRI images and the Imeka test tractogram, with segmentation methods derived from Wakana et al. and Fitzgerald et al.

Limitations

  • The authors state that inter- and intra-individual variability is greater than previously suspected and recommend larger cohorts; they also note that cited studies often have low subject numbers.
  • The authors discuss dMRI pitfalls including false positives, poor inter-protocol segmentation agreement, and orientation errors up to 90° at gray-white matter transitions; postmortem dissection cannot resolve crossing fibers or distal terminations and is biased toward elderly brains and fixation effects.
  • Evident from the text: as a review/opinion without a systematic search or quantitative synthesis, its nomenclature recommendations are expert opinion rather than empirically tested consensus.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3389/fneur.2022.794618

Cites

82 of 82 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Figure 1 Examples of coronal, sagittal, and axial MRI and DTI images. T1: T1-weighted image. B0: B0 image. FA: Fractionnal anisotropy image; Representation of the level of anisotropy in each voxel on a scale of 0 to 1, as shown in the lower left corner. RGB: Red-Green-Blue Color-coded FA image; Color-coded representation of the main direction of diffusion in each voxel, as shown in the lower right corner.
Figure 1 Examples of coronal, sagittal, and axial MRI and DTI images. T1: T1-weighted image. B0: B0 image. FA: Fractionnal anisotropy image; Representation of the level of anisotropy in each voxel on a scale of 0 to 1, as shown in the lower left corner. RGB: Red-Green-Blue Color-coded FA image; Color-coded representation of the main direction of diffusion in each voxel, as shown in the lower right corner.CC BY · PubMed Central
Figure 2 In vivo fiber tractography of the right SLF I (pink), SLF II (green), and SLF III (blue). A three-dimensional reconstruction of the three segments of the SLF is displayed at the left of the figure. The coronal sections of it (A, B, and C) are represented on the right. The dorso-ventral as well as medio-lateral localization of each sub-segment can be visualized on the coronal planes.
Figure 2 In vivo fiber tractography of the right SLF I (pink), SLF II (green), and SLF III (blue). A three-dimensional reconstruction of the three segments of the SLF is displayed at the left of the figure. The coronal sections of it (A, B, and C) are represented on the right. The dorso-ventral as well as medio-lateral localization of each sub-segment can be visualized on the coronal planes.CC BY · PubMed Central
Figure 3 In vivo fiber tractography of the right SLF I (pink) and the right cingulum (light blue) represented by volume. A three-dimensional reconstruction of the SLF I and the cingulum is displayed at the left of the figure. The coronal sections of it (A, B and C) are represented on the right. On the coronal planes, it is possible to appreciate the great proximity between the fibers of the SLF I and those of the cingulum.
Figure 3 In vivo fiber tractography of the right SLF I (pink) and the right cingulum (light blue) represented by volume. A three-dimensional reconstruction of the SLF I and the cingulum is displayed at the left of the figure. The coronal sections of it (A, B and C) are represented on the right. On the coronal planes, it is possible to appreciate the great proximity between the fibers of the SLF I and those of the cingulum.CC BY · PubMed Central
Figure 4 In vivo fiber tractography of the right SLF I (pink), SLF II (green), SLF III (blue), and AF (red) represented by volume. A three-dimensional reconstruction of these bundles is displayed at the left of the figure. The AF is slightly transparent to let appear the SLF III, being inside the latter. On the right, the coronal sections (A, B, and C) are represented. This figure confirms that the SLF III also corresponds to a sub-division of the AF. Indeed, throughout its length, the SLF III is located inside the AF.
Figure 4 In vivo fiber tractography of the right SLF I (pink), SLF II (green), SLF III (blue), and AF (red) represented by volume. A three-dimensional reconstruction of these bundles is displayed at the left of the figure. The AF is slightly transparent to let appear the SLF III, being inside the latter. On the right, the coronal sections (A, B, and C) are represented. This figure confirms that the SLF III also corresponds to a sub-division of the AF. Indeed, throughout its length, the SLF III is located inside the AF.CC BY · PubMed Central
Figure 5 Coronal section of a color-coded FA map. The green associative fibers, representing the fibers perpendicular to the plane, can be grouped into two main systems according to the classification by Mandonnet et al. (5), the SLS and the common stem for the ILS/MidLs and BLS.
Figure 5 Coronal section of a color-coded FA map. The green associative fibers, representing the fibers perpendicular to the plane, can be grouped into two main systems according to the classification by Mandonnet et al. (5), the SLS and the common stem for the ILS/MidLs and BLS.CC BY · PubMed Central
Figure 6 Schematization of the SLS and its sub-systems of the proposed nomenclature by Mandonnet et al. (5) for the human white matter association pathways.
Figure 6 Schematization of the SLS and its sub-systems of the proposed nomenclature by Mandonnet et al. (5) for the human white matter association pathways.CC BY · PubMed Central

Verification

Claims the paper makes

28 Own interpretation · 18 No full text of the sources · 6 Supported so far · 5 Partly supported · 4 Supported · 3 Couldn’t confirm · 2 Own result · 2 No basis given · 1 Mixed support · 1 Not supported · accuracy not yet measured

Show all 33 claims

  • Probably not a substantial claim. 24
  • It may state two separate claims as one. 19
37 of 37
  • The paper relies on this without support.

    The SLF is part of the longitudinal association fiber system, which lays connections between the frontal lobe and other areas of the ipsilateral hemisphere.

    “The superior longitudinal fasciculus (SLF) is part of the longitudinal association fiber system, which lays connections between the frontal lobe and other areas of the ipsilateral hemisphere.”
  • The paper relies on this without support.

    The SLF connects the perisylvian areas in the hemisphere (frontal, temporal, and parietal).

    “To put it simply, it connects the perisylvian areas in the hemisphere (frontal, temporal, and parietal).”
  • The paper relies on this without support.

    There is a clear asymmetry in speech function (left-sided characteristically) and visuospatial functioning (right-sided characteristically).

    “As there is a clear asymmetry in speech function (left-sided characteristically) and visuospatial functioning (right-sided characteristically)”
  • The paper relies on this without support.

    Some areas and connectivity routes are highly conserved amongst individuals (such as primary areas and large projection bundles), while others are more variable.

    “Although some areas and connectivity routes are highly conserved amongst individuals (such as primary areas and large projection bundles), others are more variable.”
  • The paper relies on this without support.

    The brain connectivity pattern of an individual is constantly changing, and the density of white matter changes during the development of the individual.

    “the brain connectivity pattern of an individual is constantly changing, and the density of white matter has been shown to change during the development of the individual.”
  • The paper relies on this without support.

    Individual variability had been underestimated in the past.

    “the individual variability had been underestimated in the past.”
6 of 6

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

2 of 2

Citations

Cites

Show all 81 references

Research works printed but not linked: 2

  1. Descoteaux, 2015, Wiley Encyclopedia of Electrical and Electronics Engineering (EEEE), High Angular Resolution Diffusion Imaging (HARDI)
  2. Rheault, 2016, MI-Brain, a Software to Handle Tractograms and Perform Interactive Virtual Dissection

Cited by

Sorted by citations

Metadata

Authors
Janelle, F., Iorio-Morin, C., D'amour, S., & Fortin, D.
Affiliations
Université de Sherbrooke (CA)
Corresponding author
Fortin, David
Venue
Frontiers in Neurology
Published
2022-04-27
Volume
13
Pages
794618-794618
ISSN
1664-2295 (ISSN-L)
OpenAlex
W4224927688
Cited by
189
References
81
Citations by year
2026: 57 · 2025: 61 · 2024: 45 · 2023: 25 · 2022: 1
FWCI
16.98
Type
journal article
Language
en
Open access
Locations
  • Frontiers in Neurology (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • PubMed Central (submittedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Topics
  • Health Sciences › Medicine › Radiology, Nuclear Medicine and Imaging › Advanced Neuroimaging Techniques and Applications
  • Health Sciences › Medicine › Anatomy › Classical Anatomy and Histology
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Functional Brain Connectivity Studies
Keywords
superior longitudinal fasciculus, arcuate fasciculus, frontal lobe, anatomical landmarks, hemispheric lateralization, interindividual variability, diffusion MRI, postmortem dissection, functional correlates, white matter tracts, nomenclature

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