Limits...
Distribution of axon diameters in cortical white matter: an electron-microscopic study on three human brains and a macaque.

Liewald D, Miller R, Logothetis N, Wagner HJ, Schüz A - Biol Cybern (2014)

Bottom Line: Within individual human brains, the averages were larger in the superior longitudinal fascicle than in the transitional zone between temporal and frontal lobe.A correlation was also found between the thickness of the myelin sheath and the inner axon diameter for axons whose calibre was greater than about 0.6 μm.The results are compared to white matter data in other mammals and are discussed with respect to conduction velocity, brain size, cognition, as well as diffusion weighted imaging studies.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics, Spemannstr. 38/41, 72076 , Tübingen, Germany.

ABSTRACT
The aim of this study was to obtain information on the axonal diameters of cortico-cortical fibres in the human brain, connecting distant regions of the same hemisphere via the white matter. Samples for electron microscopy were taken from the region of the superior longitudinal fascicle and from the transitional white matter between temporal and frontal lobe where the uncinate and inferior occipitofrontal fascicle merge. We measured the inner diameter of cross sections of myelinated axons. For comparison with data from the literature on the human corpus callosum, we also took samples from that region. For comparison with well-fixed material, we also included samples from corresponding regions of a monkey brain (Macaca mulatta). Fibre diameters in human brains ranged from 0.16 to 9 μm. Distributions of diameters were similar in the three systems of cortico-cortical fibres investigated, both in humans and the monkey, with most of the average values below 1 μm diameter and a small population of much thicker fibres. Within individual human brains, the averages were larger in the superior longitudinal fascicle than in the transitional zone between temporal and frontal lobe. An asymmetry between left and right could be found in one of the human brains, as well as in the monkey brain. A correlation was also found between the thickness of the myelin sheath and the inner axon diameter for axons whose calibre was greater than about 0.6 μm. The results are compared to white matter data in other mammals and are discussed with respect to conduction velocity, brain size, cognition, as well as diffusion weighted imaging studies.

Show MeSH

Related in: MedlinePlus

Electron micrograph from the corpus callosum of the macaque, showing the large range of diameters. Bar 5 
© Copyright Policy - OpenAccess
Related In: Results  -  Collection


getmorefigures.php?uid=PMC4228120&req=5

Fig7: Electron micrograph from the corpus callosum of the macaque, showing the large range of diameters. Bar 5 

Mentions: Examples of electron micrographs from the white matter are shown in Figs. 4 and 5a (region of the superior longitudinal fascicle) and Fig. 5b (region of the uncinate/inferior occipitofrontal fascicle) from the human brains and in Figs. 6 and 7 from the monkey brain. As expected, the human tissue is less well preserved than that of the monkey, as evident from the debris between the axons and partly also within the lumen of the axons, as well as the detachment of membranes from each other in some of the myelin sheaths. In spite of the lower quality of the human tissue, myelinated axonal profiles can be well identified in most cases and the shape of the myelin sheath is usually preserved well enough to indentify the inner diameter. The pictures illustrate the wide range of diameters in both monkeys and humans.Fig. 5


Distribution of axon diameters in cortical white matter: an electron-microscopic study on three human brains and a macaque.

Liewald D, Miller R, Logothetis N, Wagner HJ, Schüz A - Biol Cybern (2014)

Electron micrograph from the corpus callosum of the macaque, showing the large range of diameters. Bar 5 
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4228120&req=5

Fig7: Electron micrograph from the corpus callosum of the macaque, showing the large range of diameters. Bar 5 
Mentions: Examples of electron micrographs from the white matter are shown in Figs. 4 and 5a (region of the superior longitudinal fascicle) and Fig. 5b (region of the uncinate/inferior occipitofrontal fascicle) from the human brains and in Figs. 6 and 7 from the monkey brain. As expected, the human tissue is less well preserved than that of the monkey, as evident from the debris between the axons and partly also within the lumen of the axons, as well as the detachment of membranes from each other in some of the myelin sheaths. In spite of the lower quality of the human tissue, myelinated axonal profiles can be well identified in most cases and the shape of the myelin sheath is usually preserved well enough to indentify the inner diameter. The pictures illustrate the wide range of diameters in both monkeys and humans.Fig. 5

Bottom Line: Within individual human brains, the averages were larger in the superior longitudinal fascicle than in the transitional zone between temporal and frontal lobe.A correlation was also found between the thickness of the myelin sheath and the inner axon diameter for axons whose calibre was greater than about 0.6 μm.The results are compared to white matter data in other mammals and are discussed with respect to conduction velocity, brain size, cognition, as well as diffusion weighted imaging studies.

View Article: PubMed Central - PubMed

Affiliation: Max Planck Institute for Biological Cybernetics, Spemannstr. 38/41, 72076 , Tübingen, Germany.

ABSTRACT
The aim of this study was to obtain information on the axonal diameters of cortico-cortical fibres in the human brain, connecting distant regions of the same hemisphere via the white matter. Samples for electron microscopy were taken from the region of the superior longitudinal fascicle and from the transitional white matter between temporal and frontal lobe where the uncinate and inferior occipitofrontal fascicle merge. We measured the inner diameter of cross sections of myelinated axons. For comparison with data from the literature on the human corpus callosum, we also took samples from that region. For comparison with well-fixed material, we also included samples from corresponding regions of a monkey brain (Macaca mulatta). Fibre diameters in human brains ranged from 0.16 to 9 μm. Distributions of diameters were similar in the three systems of cortico-cortical fibres investigated, both in humans and the monkey, with most of the average values below 1 μm diameter and a small population of much thicker fibres. Within individual human brains, the averages were larger in the superior longitudinal fascicle than in the transitional zone between temporal and frontal lobe. An asymmetry between left and right could be found in one of the human brains, as well as in the monkey brain. A correlation was also found between the thickness of the myelin sheath and the inner axon diameter for axons whose calibre was greater than about 0.6 μm. The results are compared to white matter data in other mammals and are discussed with respect to conduction velocity, brain size, cognition, as well as diffusion weighted imaging studies.

Show MeSH
Related in: MedlinePlus