What Is White Matter in the Brain?

Compairng Brain Scans/ Geri Lavrov Moment/ Getty Images.

White Matter: What Is It?

Think of the brain like a computer system, and it might be easier to understand. According to the UC Davis Health System, the gray matter (nerve cells) of our brain is the computer and the white matter is the cables that connect everything together and transmit signals.

Want more of a biological explanation? White matter is tissue in the brain composed of nerve fibers. The fibers (called axons) connect nerve cells and are covered by myelin (a type of fat).

The myelin is what gives white matter its white color. Myelin speeds up the signals between the cells, enabling the brain cells to quickly send and receive messages. It also provides insulation for the fibers, preventing the brain from short-circuiting.

White matter makes up about half of the brain.

What's the Relationship between Dementia and White Matter?

Some research has found that abnormalities in white matter was present on imaging studies of the brain prior to the development of the symptoms of Alzheimer's disease. Research has also demonstrated the presence of white matter lesions prior to mild cognitive impairment, a condition that carries an increased risk for Alzheimer's disease.

What Are White Matter Hyperintensities?

White matter hyperintensities is a term you might hear used to describe spots in the brain that show up on MRIs as a bright white areas. According to Charles DeCarli, the director of UC Davis Alzheimer's Disease Center, these areas may indicate some type of injury to the brain, perhaps due to decreased blood flow in that area.

The presence of white matter hyperintensities have been correlated with a higher risk of stroke, which can lead to vascular dementia.

About.com's Neurology expert Peter Pressman, MD, describes these white matter spots in more detail here: What Are These Spots on My MRI?

Related Reading


Current Opinion in Psychiatry. 2013 May;26(3):244-51. doi: 10.1097/YCO.0b013e32835ed6e8. Is Alzheimer's a disease of the white matter?. http://www.ncbi.nlm.nih.gov/pubmed/23493128

Medline Plus. January 13, 2013. White Matter of the Brain. http://www.nlm.nih.gov/medlineplus/ency/article/002344.htm

 Medline Plus. February 27, 2013. Gray and white matter of the brain. http://www.nlm.nih.gov/medlineplus/ency/imagepages/18117.htm

Neurology August 21, 2012 vol. 79 no. 8 741-747 . OHSU. Paper of the Month: White matter change as early MRI markers of cognitive decline. http://www.ohsu.edu/xd/education/schools/school-of-medicine/about/school-of-medicine-news/research-news/paper-92512.cfm

Therapeutic Advances in Neurological Disorders. 2012 Sep; 5(5): 267–277. White matter dementia. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3437529/

UC Davis Health System. Department of Neurology. White Matter Matters. Accessed April 28, 2015. http://www.ucdmc.ucdavis.edu/neurology/newsroom/white_matter_feature.html

VU University Amsterdam. Accessed April 28, 2015. Center for Children with White Matter Disorders. http://www.vumc.com/branch/Children-White-Matter-Disorders/419542/


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