White Matter: Structural and Functional Roles in Health and Disease
This article reviewed the literature regarding structural and functional roles of white matter in health and disease. It was found that white matter has a structure consisting of bundles that work to connect areas of gray matter in the brain. These bundles also transmit nerve impulses between neurons. Myelin, the outer coating envelop acts as an insulator and permits the jumping of electrical signals instead of passing through the axon. From a functional point of view, white matter carries the messages among various areas of gray matter through the central nervous system. The white matter is called white due to the presence of the fatty material (myelin) that makes the outer layer of axons, and accelerates the transmission of nerve signals. We showed the impacts of alcohol use and other diseases such as Alzheimer disease on white matter. Taken together, white matter has central roles in health and disease.
White matter, myelin, alcohol, Alzheimer disease, axon.
Alkhatib, A.J., 2019. White Matter: Structural and Functional Roles in Health and Disease. PSM Biol. Res., 4(1): 17-19.
The white matter is composed of fibers with ascending and descending orientation that are either originating in or projecting to the cortex (Zola-Morgan, 1995; Jiang et al., 2017). White matter is consisted of bundles that work to connect areas of gray matter in the brain. These bundles also transmit nerve impulses between neurons (O’Muircheartaigh and Jbabdi, 2018). Myelin, the outer coating envelop acts as an insulator and permits the jumping of electrical signals instead of passing through the axon (Klein and Thorne, 2007; Fields, 2014). The volume of white matter in women is generally less than that in males in either terms of volume and myelinated axons. As age increases, white matter volume decreases (Lisbeth et al., 2003; Kanaan et al., 2012).
White matter carries the messages among various areas of gray matter through the central nervous system. The white matter is called white due to the presence of the fatty material (myelin) that makes the outer layer of axons, and accelerates the transmission of nerve signals (Colby, 2012). The development of white matter continues and reaches its peak in middle age (Lisbeth et al., 2003, McEvoy et al., 2018). A very well- known example illustrating the effects of disease on white matter is multiple sclerosis (MS) in which the myelin surrounding the axon is damaged by inflammatory processes (Kim et al., 2006; Klawiter et al., 2011). The use of alcohol leads to disorders that are accompanied with decreased white matter volume (Monnig et al., 2013). Evidence from studies on animals demonstrated that alcohol induced the volume of white matter through breaking down oligodendrocytes that act to keep myelin (Alfonso-Loeches et al., 2012).
Some changes may occur in white matter, known as amyloid plaques are associated with Alzheimer’s disease besides other neurodegenerative diseases (Albert et al., 2011). The injuries affecting white matter may be reversible (Kinnunen et al., 2011). A group of changes are usually occurred in white matter with age such as leukoaraiosis are likely to occur as a result of various conditions including loss of myelin, axonal loss, and a breakdown of the blood –brain barrier (Gupta et al., 2012).
Neuroimaging can be used to detect the volume changes in white matter. Diffusion tensor imaging (DTI) was used to investigate changes in the volume of white matter under the effect of learning a new motor task (e.g. juggling) (Scholz et al., 2009). It was demonstrated for the first time that motor learning is associated with changes of white matter. Another study by Sampaio-Baptista (2013) showed that changes in white matter associated with motor learning are due to increase in myelinations.
White matter has important structural and functional roles in health and disease and may have future therapeutic implications.
CONFLICT OF INTEREST
All the authors have declared that no conflict of interest exists.
Albert, M.S., DeKosky, S.T., Dickson, D., Dubois, B., Feldman, H.H., Fox, N., et al. 2011. The diagnosis of mild cognitive impairment due to Alzheimer’s disease: Recommendations from the National Institute on Aging-Alzheimer’s Association workgroups on diagnostic guidelines for Alzheimer’s disease. Alzheimer’s Dement., 7(3): 270-9.
Alfonso-Loeches, S., Pascual, M., Gómez-Pinedo, U., Pascual-Lucas, M., Renau-Piqueras, J., Guerri, C., 2012. Toll-like receptor 4 participates in the myelin disruptions associated with chronic alcohol abuse. Glia., 60(6): 948–64.
Colby, J.B., 2012. Development of human brain connectivity in health and disease. Ph. D in Biomedical Engineering, University of California, Los Angeles.
Fields, R.D., 2014. Myelin—More than Insulation. Science, 344(6181): 264–266. doi: [10.1126/science.1253851].
Gupta, A., Nair, S., Schweitzer, A.D., et al. 2012. Neuroimaging of Cerebrovascular Disease in the Aging Brain. Aging and Dis., 3(5): 414-425.
Jiang, Y., et al., 2017. White-matter functional networks changes in patients with schizophrenia. NeuroImage, https://doi.org/10.1016/j.neuroimage.2018.04.018.
Kanaan, R. A., Allin, M., Picchioni, M., Barker, G. J., Daly, E., Shergill, S. S., Woolley, J, McGuire, P. K., 2012. Gender differences in white matter microstructure. PloS One, 7(6): e38272.
Kim, J.H., Budde, M.D., Liang, H., Klein, R.S., Russell, J.H., Cross, A.H., Song, S., 2006. Detecting axon damage in spinal cord from a mouse model of multiple sclerosis. Neurobiol. Dis., 21(3): 626–32.
Kinnunen, K.M., Greenwood, R., Powell, J.H., Leech, R., Hawkins, P.C., Bonnelle, V., Sharp, D.J., 2011. White matter damage and cognitive impairment after traumatic brain injury. Brain, 134(2): 449–463.
Klawiter E.C., Schmidt R.E., Trinkaus K., Liang H.F., Budde M.D., Naismith R.T., Song S.K., Cross A.H., Benzinger T.L., 2011. Radial diffusivity predicts demyelination in ex vivo multiple sclerosis spinal cords. NeuroImage. 55:1454–1460.
Klein, S.B., Thorne, B.M., 2007. Biological Psychology. Worth Publishers: New York.
Marner, L., Nyengaard, J.R., Tang, Y., Pakkenberg, B., 2003. Marked loss of myelinated nerve fibers in the human brain with age. J. Comp. Neurol., 462(2): 144–52.
McEvoy, L.K., Fennema-Notestine, C., Elman, J.A., Eyler, L.T., Franz, C.E., Hagler, D.J., Hatton, S.N., Lyons, M.J., Panizzon, M.S., Dale, A.M., Kremen, W.S., 2018. Alcohol intake and brain white matter in middle aged men: Microscopic and macroscopic differences. Neuroimage. Clin., 18: 390-398. doi:10.1016/j.nicl.2018.02.006
Monnig, M.A., Tonigan, J.S., Yeo, R.A., Thoma, R.J., McCrady, B.S., 2013. White matter volume in alcohol use disorders: A meta-analysis. Addict. Biol., 18(3): 581–92.
Sampaio-Baptista, C., Khrapitchev, A.A., Foxley, S., Schlagheck, T., Scholz, J., Jbabdi, S., Deluca, G.C., Miller, K.L., Taylor, A., Thomas, N., Kleim, J., Sibson, N.R., Bannerman, D., Johansen-Berg, H., 2013. Motor Skill Learning Induces Changes in White Matter Microstructure and Myelination. J. Neurosci., 33(50): 19499–503.
Scholz, J., Klein, M.C., Behrens, T.E., Johansen-Berg, H., 2009. Training induces changes in white-matter architecture. Nat. Neurosci., 12(11): 1370–1.
Zola-Morgan, S., 1995. Localization of brain function – the legacy of Franz Joseph Gall (1758-1828). Ann. Rev. Neurosci., 18: 359-383.
Author: Ahed J Alkhatib
Published Online: Oct. 22, 2018
Article Type: Mini-Review