Mapping of fiber orientation in human internal capsule by means of polarized light and confocal scanning laser microscopy

https://doi.org/10.1016/S0165-0270(99)00132-6Get rights and content

Abstract

The nervous fibers in the human internal capsule were mapped according to their three-dimensional orientation. Four human cadaver brains were cut into comparable and standardized sections parallel to the ACPC-plane, stained with DiI, and analyzed using a combination of confocal and polarized light microscopy at the same time. This combination provides information about the structure and orientation of the fibers in great detail with confocal microscopy, and information about the localization and orientation of long myelinated fiber tracts with polarization microscopy. The internal capsule was parcellated in the areas CI 1 to CI 4 containing fibers of distinct orientation and structure, which enriches the macroscopically definable parcellation in the anterior and posterior limb. Fibers of the anterior thalamic peduncle intermingle with frontopontine tract fibers. Single fibers connect the caudate and the lentiform nucleus. The pyramidal tract is located in the anterior half of the posterior limb intermingled with fibers of the superior thalamic peduncle. Parietooccipitopontine fibers are located in the posterior part of the posterior limb. The slopes of the different systems of fibers change continuously in the anterior–posterior direction of the internal capsule. Using the 3D orientation of fibers as a criterion for parcellation, as well as the description of bundles as a collection of fibers belonging to particular tracts leads to a more function-related description of the anatomy of the internal capsule. The method can be used for interindividual, sex- or age-related comparisons of particular systems of fibers.

Introduction

The fiber architecture especially of the white matter in the human brain is presently the focus of interest. Many neurologic diseases affect the cerebral white matter, and modern imaging procedures such as magnetic resonance imaging (MRI) provide detailed visual information about the white matter. Anatomical knowledge about nervous fibers was achieved earlier by fiber preparations (Ebeling and Reulen, 1992), myelogenic studies (Kretschmann, 1988) and by observations after brain injury (Fries et al., 1993).

We were able to demonstrate the orientation and texture of the nervous fibers to influence the value of impedance measurements, and so an online verification of the needle’s position in a stereotactic procedure can be performed (Axer et al., 1998). In addition, the orientation of nervous fibers can be visualized by modern MRI procedures (Curnes et al., 1988, Douek et al., 1991, Peled et al., 1998). Nevertheless, a detailed anatomical mapping of fiber orientations in the adult human brain is difficult to assess. Our aim was to perform a mapping of the orientation of the fibers in the internal capsule. Thus we wanted to find out how anatomically defined fiber tracts are oriented in the white matter. The method should give information about fiber texture, fiber orientation and identification of specific fiber tracts.

Therefore we used the combination of confocal laser microscopy and polarized light microscopy. The confocal laser microscope allows information to be collected from well-defined optical sections. This is done by a sequential illumination which is focused on one volume element of the specimen at a time (Wright et al., 1993). This way stacks of optical sections can be produced, which allow three-dimensional reconstruction of the fiber texture and provide good information about the orientation of the fibers at high resolution.

Polarized light microscopy can selectively visualize anisotropic structures. In polarization microscopy, optically polarized light passes through a sample of tissue and into a second polarizer (analyzer), which polarizes light in a perpendicular plane with respect to the first polarizer. Birefringence is able to twist some of the light so that it can pass through the analyzer and be imaged. The birefringence of the nervous tissue has been well known for a long time (Schmidt, 1923, Schmidt, 1924, Schmitt and Bear, 1936, Kretschmann, 1967, Wolman, 1975). As the presence of anisotropy indicates polarity and order, polarization microscopy can be used to visualize long fiber tracts in the brain (Fraher and MacConnaill, 1970, Miklossy and Van der Loos, 1991). The orientation of the fibers influences the transmission of plane-polarized light at different velocities at different azimuths.

The combination of both techniques allowed us to obtain detailed information of the fiber structure and orientation with confocal microscopy and to collect information about the localization and orientation of long myelinated fiber tracts with polarized light microscopy.

The internal capsule in the adult human brain represents a collection of different systems of fibers closely located in a small space. It is a structure of high clinical importance, since the fibers of the pyramidal tract are located here. Nevertheless the exact location of the pyramidal tract in the internal capsule was a matter of dispute for decades (Maurach and Strian, 1981).

Section snippets

Macroscopic preparation

Four human cadaver brains without macroscopically definable pathology and without a history of neurologic or psychiatric disease were fixed in 4% aqueous formalin solution and macroscopically prepared. The meninges were removed and the brains cut in the median-sagittal plane. Important landmarks were identified on the median surface of the hemispheres: the anterior and posterior commissure, the interventricular foramen of Monro and the internal cerebral vein (or the tela choroidea ventriculi

Results

In polarization microscopy, the detectable signal depends on the order and the inclination of the fibers. In particular, parallel, horizontally cut fibers give a bright signal at a special azimuth whereas the signal decreases after rotation of 45°. The steeper these tracts of fibers are, the less bright the signal is. Thus different fiber tracts of different orientation and order produce areas of different brightness. In low magnification, the polarization picture provides information about the

Methodological considerations

Traditionally the internal capsule is divided into the anterior limb, the genu and the posterior limb (Dejerine, 1901). The areas occupied by the distinct bundles of fibers differ from the borders of the macroscopically defined parcellation of the internal capsule. In his classical description, Vogt (1902) subdivided the posterior limb into three parts according to the intensity of the Weigert staining. This subdivision, however, does not take care of the orientation of the fibers.

The central

Acknowledgements

We would like to thank Petra Ibold and Anita Agbedor for their technical assistance.

References (61)

  • S. Peled et al.

    Magnetic resonance imaging shows orientation and asymmetry of white matter fiber tracts

    Brain Res.

    (1998)
  • J. Tomasch

    The numerical capacity of the human cortico-ponto-cerebellar system

    Brain Res.

    (1969)
  • J.A. Vilensky et al.

    Corticopontine projections from the cingulate cortex in the rhesus monkey

    Brain Res.

    (1981)
  • R. Wiesendanger et al.

    An anatomical investigation of the corticopontine projection in the primate (Macaca fascicularis and Saimiri sciureus)—II. The projection from frontal and parietal association areas

    Neuroscience

    (1979)
  • S.J. Wright et al.

    Introduction to confocal microscopy and three-dimensional reconstruction

    Methods Cell Biol.

    (1993)
  • H. Axer et al.

    Terminology of the thalamus and its representation in a part-whole relation

    Methods Inf. Med.

    (1994)
  • H. Axer et al.

    Semiquantitative analysis of myelin content in human central nervous tissue with methods of fuzzy geometry

  • H. Axer et al.

    Comparison of tissue impedance measurements with nerve fiber architecture in human telencephalon: value in identification of intact subcortical structures

    J. Neurosurg.

    (1999)
  • E. Beck

    The origin, course and termination of the prefronto-pontine tract in the human brain

    Brain

    (1950)
  • J. Bogousslavsky et al.

    Capsular genu syndrome

    Neurology

    (1990)
  • P. Brodal

    The corticopontine projection in the rhesus monkey. Origin and principles of organization

    Brain

    (1978)
  • P. Brodal

    The cerebropontocerebellar pathway: Salient features of its organization

    Exp. Brain Res.

    (1982)
  • M.B. Carpenter

    Anatomy and physiology of the basal ganglia

  • J.T. Curnes et al.

    MR imaging of compact white matter pathways

    AJNR Am. J. Neuroradiol.

    (1988)
  • R.A. Davidoff

    The pyramidal tract

    Neurology

    (1990)
  • N.A.H. Dawney et al.

    Somatotopic analysis of fibre and terminal distribution in the primate corticospinal pathway

    Dev. Brain Res.

    (1986)
  • J. Dejerine

    Anatomie des centres nerveux

    (1901)
  • P. Douek et al.

    MR color mapping of myelin fiber orientation

    J. Comput. Assist. Tomogr.

    (1991)
  • U. Ebeling et al.

    Subcortical topography and proportions of the pyramidal tract

    Acta Neurochir.

    (1992)
  • R.N. Englander et al.

    Location of the human pyramidal tract in the internal capsule: Anatomic evidence

    Neurology

    (1975)
  • Cited by (105)

    • Four Deep Brain Stimulation Targets for Obsessive-Compulsive Disorder: Are They Different?

      2021, Biological Psychiatry
      Citation Excerpt :

      Axons from each cortical area remain clustered as they enter and travel through the ALIC. They are organized into two intertwined bundles: those that exit the capsule to the thalamus, and those that continue to the brainstem (24,39). The ALIC is organized topologically and can be segmented into five regions based on positions of PFC/ACC fibers within it (Figure 1A) (25).

    View all citing articles on Scopus
    View full text