Characterizing axonal myelination within the healthy population: a tract-by-tract mapping of effects of age and gender on the fiber g-ratio

Cercignani, Mara, Guilietti, Giovanni, Dowell, Nick G, Gabel, Matt, Broad, Rebecca, Leigh, P. Nigel, Harrison, Neil A and Bozzali, Marco (2016) Characterizing axonal myelination within the healthy population: a tract-by-tract mapping of effects of age and gender on the fiber g-ratio. Neurobiology of Aging, 49. pp. 109-118. ISSN 0197-4580

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Abstract

The g-ratio, equal to the ratio of the inner-to-outer diameter of a myelinated axon, is associated with the speed of conduction, and thus reflects axonal function and integrity. It is now possible to estimate an “aggregate” g-ratio in vivo using MRI. The aim of this study was to assess the variation of the MRI-derived fiber g-ratio in the brain of healthy individuals, and to characterize its variation across the lifespan. Thirty-eight healthy participants, aged between 20 and 76, were recruited. Whole-brain g-ratio maps were computed and analyzed voxel-wise. Median tract g-ratio values were also extracted. No significant effect of gender was found, whereas age was found to be significantly associated with the g-ratio within the white matter. The tract-specific analysis showed this relationship to follow a nearly-linear increase, although the slope appears to slow down slightly after the 6th decade of life. The most likely interpretation is a subtle but consistent reduction in myelin throughout adulthood, with the density of axons beginning to decrease between the 4th and 5th decade.

Item Type: Article
Keywords: Myelination; White matter; Axonal conduction; Lateralization
Schools and Departments: Brighton and Sussex Medical School > Neuroscience
Subjects: R Medicine
Depositing User: Patricia Butler
Date Deposited: 19 Dec 2016 17:28
Last Modified: 21 Jul 2017 19:36
URI: http://sro.sussex.ac.uk/id/eprint/65954

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