White Matter Function & Disorders - Brain Anatomy Explained

What Is White Matter? Role in Cognition & Neurological Conditions

The human brain is the most intricate and complex organ in the body, and its function relies on two important types of tissues: the white matter and the grey matter. Grey matter is involved in the processing and interpretation of information; the white matter acts as a communication centre for the brain.

What is the Main Function of White Matter?

The function of the white matter is to provide communication in the brain. It conducts nerve impulses between brain cells (neurones), especially long-distance transmissions. Moreover, it functions like a relay system, rapidly transmitting messages from sensory organs or internal thoughts to their respective destinations for processing and response.

This role is particularly significant in activities involving inter-regional coordination in the brain, like learning, problem-solving, and motor control. For instance, when you choose to move your arm, the decision-making centres in your frontal lobe (grey matter) must communicate with the motor cortex and then with your spinal cord for the movement to occur.

White matter efficiency directly influences cognitive speed and working memory. Researchers have also found that greater white matter integrity typically enhances cognitive function, accelerates processing speeds, and strengthens mental resilience.

What is White Matter Composed of?

Myelinated axons, extensions of neurones that help transport electrical signals, constitute the white matter. In the central nervous system, each axon is wrapped with a myelin sheath derived from a kind of glial cell known as an oligodendrocyte. Myelin functions like insulation around an electrical wire, allowing impulses to travel quickly and efficiently.

Besides myelinated axons, other supportive cells are also found in the white matter:

• Glial cells, such as astrocytes and microglia, support neuronal health and respond to injury.
• Blood vessels and capillaries bring oxygen and nutrients to tissues.
• Extracellular matrix proteins ensure structuring.

These glial cells bundle white matter fibres into tracts that connect different regions of the brain and spinal cord. For example, the corpus callosum joins two cerebral hemispheres, and the internal capsule joins the cerebral cortex to the brainstem and spinal cord.

How Does White Matter Differ from Grey Matter?

The difference between white matter and grey matter is given in the following table:

 What Conditions Affect White Matter?

Several neurological diseases and disorders can damage the white matter, resulting in cognitive abilities, motor disorders, or sensory injuries. Typical ailments are given below:

1. Multiple Sclerosis (MS)

It occurs when your immune system attacks myelin sheaths, disrupting signal transmission and leading to muscle weakness, fatigue, and coordination difficulties.

2. Leukodystrophies

This is a category of uncommon genetic disorders which impact the development or preservation of myelin.

3. Vascular Dementia

It is a result of small vessel disease, causing a decline in cognitive ability owing to inadequate blood flow to the white matter.

4. Traumatic Brain Injury (TBI)

May shear white matter tracts, which interrupt communication between brain regions.

5. White Matter Hyperintensities (WMHs)

Observed in the ageing process and linked to an increased possibility of stroke, depression, and dementia.

6. Cerebral Palsy

Commonly includes white matter destruction during the brain’s early formation, especially among premature babies.

7. Neurodegenerative Diseases

Degeneration of white matter partly causes conditions such as Alzheimer’s disease and Parkinson’s.

How is White Matter Damage Diagnosed?

The diagnosis of white matter damage is usually carried out with the help of neuroimaging methods that enable a clinician to see the interior structure of the brain:

Magnetic Resonance Imaging (MRI)

MRI is a method for detecting abnormalities of the white matter. T2-weighted and FLAIR (Fluid Attenuated Inversion Recovery) sequences are particularly effective in identifying lesions of the white matter.

Diffusion Tensor Imaging (DTI)

An advanced MRI sequence that allows the visualisation of the diffusion of water molecules along the white matter fibres, providing information about the integrity of the connections and their direction.

Computed Tomography (CT)

Sometimes performed, more often in an acute care situation, such as trauma or stroke, but less sensitive than MRI to white matter.

Neurological Testing

Cognitive and motor tests can also be used to identify white matter injury where imaging studies are inconclusive. They are tests of memory, reaction time, coordination and speech fluency.

Biopsy or Genetic Testing

Rarely, when the disorder is likely inherited, as in the case of leukodystrophies, a brain biopsy or genetic testing may be required.

White matter in the brain consists of myelinated nerve fibres that facilitate communication between different brain regions. It plays a key role in coordination, learning, and overall brain function, supporting efficient transmission of electrical signals throughout the nervous system.