Functional Anatomy of the Inferior Longitudinal Fasciculus: From Historical Reports to Current Hypotheses

The inferior longitudinal fasciculus (ILF) is a long-range, associative white matter pathway that connects the occipital and temporal-occipital areas of the brain to the anterior temporal areas. In view of the ILF’s anatomic connections, it has been suggested that this pathway has a major role in a relatively large array of brain functions. Until recently, however, the literature data on these potential functions were scarce. Here, we review the key findings of recent anatomic, neuromodulation, and neuropsychological studies. We also summarize reports on how this tract is disrupted in a wide range of brain disorders, including psychopathologic, neurodevelopmental, and neurologic diseases. Our review reveals that the ILF is a multilayered, bidirectional tract involved in processing and modulating visual cues and thus in visually guided decisions and behaviors. Accordingly, sudden disruption of the ILF by neurologic insult is mainly associated with neuropsychological impairments of visual cognition (e.g., visual agnosia, prosopagnosia, and alexia). Furthermore, disruption of the ILF may constitute the pathophysiologic basis for visual hallucinations and socio-emotional impairments in schizophrenia, as well as emotional difficulties in autism spectrum disorder. Degeneration of the ILF in neurodegenerative diseases affecting the temporal lobe may explain (at least in part) the gradual onset of semantic and lexical access difficulties. Although some of the functions mediated by the ILF appear to be relatively lateralized, observations from neurosurgery suggest that disruption of the tract’s anterior portion can be dynamically compensated for by the contralateral portion. This might explain why bilateral disruption of the ILF in either acute or progressive disease is highly detrimental in neuropsychological terms

Reconstruction of white matter tracts from dissection and coregistration with post mortem MRI for the comparison to cerebral MRI diffusion tractography

La connaissance de la morphologie des faisceaux de fibres blanches, qui connectent des régions cérébrales distantes, est indispensable à la compréhension du fonctionnement cérébral. La tractographie par IRM de diffusion reconstruit indirectement cette anatomie à partir d'algorithmes mathématiques complexes. Après une revue des méthodes proposées pour la validation de la tractographie, nous proposons une méthode originale basée sur la reconstruction 3D de faisceaux disséqués. Notre méthode, FIBRASCAN, utilise des acquisitions itératives de surface en cours de dissection. Les faisceaux étaient segmentés sur chaque surface puis reconstruits par empilement. Un support rigide permettait le recalage entre surfaces puis vers l'IRM. Nous avons démontré la précision de chaque étape de reconstruction, et sa faisabilité sur plusieurs faisceaux. Dans la dernière partie de ce travail, la structure des fibres blanches et les modifications induites par la préparation et la dissection sont explorées en microscopie électronique. Nous avons montré que la dissection préservait la structure des axones et peut ainsi être considérée comme un outil de validation de la tractographie.The knowledge of the morphology of white matter fiber tracts, which connect distant cerebral areas, is essential to better understand brain functions. Diffusion MR tractography indirectly reconstructs this anatomy using complex mathematical algorithms. After a review of the existing methods for tractography validation, we propose an original method based on 3D reconstruction of dissected tracts. Our method, FIBRASCAN, used iterative surface acquisitions during dissection. The tracts were segmented on each surface and then reconstructed by stacking these surfaces. A rigid support allowed registration between surfaces and then registration to MRI. We demonstrated the accuracy of each reconstructing step, and the feasibility of our method on several tracts. In the last part of this work, the structure of white matter fibers and the changes induced by preparation and dissection were investigated using electron microscopy. We showed that dissection preserves the structure of axons and can thus be considered as a validation tool for tractography

Développement d'une technique de suivi de dissection des fibres blanches cérébrales selon la méthode de Klingler (reconstruction tridimensionnelle du faisceau longitudinal supérieur)

TOURS-BU Médecine (372612103) / SudocSudocFranceF

Gross Anatomy of the Human Insula

This is the post-print version of the following article: "Gross Anatomy of the Human Insula", which has been published in final form at https://link.springer.com/chapter/10.1007%2F978-3-319-75468-0_2International audienceWhen the lips of the lateral fissure are separated from each other, a new group of sulci and gyri appear. They are ar-rayed together in the form of an island, which is the reason why the German anatomist Johann Christian Reil named them "the insular lobe". Bordered by the limiting sulci, its general form resembles that of an oblique pyramid with a triangular base and low height. Although some anatomical variation exists, the insu-la presents a systematizable internal organization and well-defined anatomical relationships with deep and superficial cere-bral structures, such as the extreme capsule and the cerebral opercula. In this chapter we review concepts of the insular morphology that are important to the fields of neurosurgery and neuroimaging

Functional Anatomy of the Inferior Longitudinal Fasciculus: From Historical Reports to Current Hypotheses

International audienceThe inferior longitudinal fasciculus (ILF) is a long-range, associative white matter pathway that connects the occipital and temporal-occipital areas of the brain to the anterior temporal areas. In view of the ILF’s anatomic connections, it has been suggested that this pathway has a major role in a relatively large array of brain functions. Until recently, however, the literature data on these potential functions were scarce. Here, we review the key findings of recent anatomic, neuromodulation, and neuropsychological studies. We also summarize reports on how this tract is disrupted in a wide range of brain disorders, including psychopathologic, neurodevelopmental, and neurologic diseases. Our review reveals that the ILF is a multilayered, bidirectional tract involved in processing and modulating visual cues and thus in visually guided decisions and behaviors. Accordingly, sudden disruption of the ILF by neurologic insult is mainly associated with neuropsychological impairments of visual cognition (e.g., visual agnosia, prosopagnosia, and alexia). Furthermore, disruption of the ILF may constitute the pathophysiologic basis for visual hallucinations and socio-emotional impairments in schizophrenia, as well as emotional difficulties in autism spectrum disorder. Degeneration of the ILF in neurodegenerative diseases affecting the temporal lobe may explain (at least in part) the gradual onset of semantic and lexical access difficulties. Although some of the functions mediated by the ILF appear to be relatively lateralized, observations from neurosurgery suggest that disruption of the tract’s anterior portion can be dynamically compensated for by the contralateral portion. This might explain why bilateral disruption of the ILF in either acute or progressive disease is highly detrimental in neuropsychological terms

From Vesalius to tractography

International audienceVesalius rejected the existence of the rete mirabile in human not only because he was a talented anatomist butalso because he accepted and had the courage to fight the dominant tradition inherited from Galen. Such difficulties in the scientific approach obviously remain vivid, and should not be forgotten despite the development of modern tools for studying brain morphologyand function.History of medicine - Neuroanatomy - Whitematter - Anatomy - Brai

French normative data for the Complex Rey Figure Test in healthy subjects aged over 80 years

International audienceTo our knowledge, there are few studies on the cognitive assessment of very old people, over 80 years old in the French population. However, this population, which currently represents 6% of the French population, is particularly affected by dementia (nearly 30% of the population is over 90 years old according to Gil in 2018) and is expected to double by 2080 (Eurostat, 2021). Rey's complex figure test is commonly used to assess visual memory, motor functions, perceptual abilities, and executive functions. This test is part of the minimal neuropsychological assessment to participate in the diagnosis of neurodegenerative diseases such as Alzheimer's disease, as recently recalled by Guichard-Gomez and Hahn (2020). There are many normative data in adults (Fastenau et al, 1999; Casanova et al, 2009; Tremblay et al, 2015; Darwish et al, 2018; Tsatali et al, 2022) but the age group of over 80 years is not well specified. We present here the results of a study of 109 healthy French subjects, aged over 80 years, from the FIBRATLAS cohort. Rey's figure was thus proposed in copy, immediate recall, and delayed recall. We considered both score and time of completion of the 3 tasks. The impact of age and education on test performance was examined. The analysis showed a gender effect for all 3 tasks. There was an effect of education on the completion time of the figure copying task and on the delayed recall score. Based on these analyses, we propose to use in clinical practice, for a French-speaking population of more than 80 years old, normative data established in percentiles, considering gender and education level

Evaluation des fonctions cognitives chez le sujet très âgé à partir de la cohorte Fibratlas

International audienc

Acquisition, visualisation 3D et interactions pour le suivi de dissection

International audienceNous présentons la conception d'un système complet de suivi de dissection anatomique depuis l'acquisition des données jusqu'à la visualisation interactive et immersive. L'acquisition est réalisée en deux temps, d'abord à l'aide d'un scanner laser pour obtenir une surface 3D, puis ensuite avec un appareil photographique haute résolution pour la texture. Cette dernière est ensuite plaquée sur la surface 3D pour obtenir une surface texturée. Ce processus d'acquisition est répété sur plusieurs étapes de la dissection en cours. Les surfaces sont ensuite recalées entre elles grâce à des repères fixes. L'expert peut alors explorer les données avec du matériel d'interaction en y étant immergé grâce à la visualisation 3D stéréoscopique. Un outil d'étiquetage interactif est proposé à l'expert anatomiste afin d'identifier des zones d'intérêt sur chaque surface acquise. Une reconstruction 3D de la structure étudiée sera effectuée à partir des zones étiquetées sur l'ensemble des surfaces acquises; l'objectif final étant la constitution de vérités terrain en vue de comparer et valider des données issues d'IRM