Published August 06, 2023 by

What is Gray Matter and White Matter? Their Functions, Differences between Gray and White Matter

The human brain is an organ that weighs 1.3 kg and remains largely an enigma. However, most people are aware of the grey matter in the brain, which is important for cognitive processes including memory, thinking, and learning.

The mass or gray matter designates, more specifically, regions scattered throughout the brain in which nerve cells, known as neurons, are concentrated. The cerebral cortex, a thin layer of grey matter on the surface of the brain, is the area thought to be most crucial for cognition. 

But the other half of the brain - the white matter - is often overlooked. The white matter lies below the cortex and in deeper regions of the brain. Where it is present, it connects gray matter neurons to each other.


This lack of recognition, in large part, comes from the difficulty of studying the mass or white matter.

Because it is located beneath the surface of the brain, even the highest imaging technology cannot easily reveal its details. But recent discoveries, made possible by advances in brain imaging and autopsy examinations, are beginning to show researchers the importance of white matter. 

Axons, which resemble lengthy wires and conduct electrical information, make up the many billions of cells that make up white matter. Consider axons as the extended tails that function as the neurons' extensions.

Synapses are junctions where axons join neurons together. The exchange of information between neurons occurs here. 

Axons gather in bundles or branches, which extend throughout the brain. If they were aligned, their total length in a single human brain would be about 136 thousand kilometers. 

Many axons are insulated with myelin, a layer composed mainly of fat that speeds up to 100 times the electrical signaling, or communication, between neurons. This increased speed is fundamental to all brain function and is one of the reasons for the unique mental abilities of Homo sapiens. 

While there is no doubt that our large brains are a consequence of the addition of neurons that occurred during evolution, the increase in white matter in the evolutionary process was even greater.

This little-known fact has profound consequences. The increase in the volume of white matter - mainly the myelin sheaths that cover axons - enhances the efficiency of gray matter neurons to optimize brain functions. 

Imagine a country where all cities function independently but are not connected by roads, wires, internet or other connections. This would be a similar scenario to the brain without the white matter. 

Higher functions, such as language and memory, are organized into networks in which regions of gray matter are connected by branches of white matter. The more extensive and efficient these connections are, the better the brain functions.

Importance of White Matter

The central nervous system's white matter is in charge of information transmission. The name it receives derives from the color that the myelin sheaths, which are white in color, give this substance. Myelin makes electrical information travel quickly from one neuron to another, coating its axons. 

In the brain, the white matter is located underneath the gray matter, which is the cerebral cortex. In the spinal cord, it is found on the outside, covering the gray matter. It is made up of axons that send sensory and motor information to the corresponding place. Although, initially, it was attributed the function of disseminating information, it also seems to be involved in other processes.

White Matter and Alzheimer's 

Considering its essential role in connections between brain cells, white matter lesions can impair any aspect of cognitive or emotional function. 

Numerous brain illnesses involve white matter dysfunction, which can be severe enough to lead to dementia. These illnesses frequently involve myelin destruction, and when the illness or injury is more serious, axons can also sustain damage. 

My coworkers and I coined the term "white matter dementia" to describe this illness more than 30 years ago. In this condition, the dysfunctional white matter is no longer functioning properly as a connection, which means that the gray matter is not able to act continuously and synchronously. Essentially, the brain has disconnected from itself.

Equally important is the possibility that white matter disorders influence many diseases that are currently believed to have gray matter origin. 

Some of these diseases insist on defying our understanding. I suspect, for example, that white matter lesions may be critical in traumatic brain injuries and in the early stages of Alzheimer's disease. 

Alzheimer's is the most common type of dementia in elderly individuals. It can impair cognitive functions and steal people's very identity. And there is no cure or effective treatment for it. 

Ever since Alois Alzheimer observed gray matter proteins - known as amyloid and tau - in 1907, neuroscientists have believed that the accumulation of these proteins is the core problem behind Alzheimer's disease. Even so, many drugs that eliminate these proteins do not stop patients' cognitive decline.

Recent discoveries increasingly indicate that white matter lesions prior to the accumulation of these proteins may be the true cause of the disease. As the brain ages, it often experiences a gradual loss of blood flow, caused by narrowing of the vessels that carry blood from the heart. And the lower blood flow has a strong impact on the white matter. 

It is important to note that there is increasing evidence that inherited forms of Alzheimer's also have early white matter abnormalities. This suggests that preserving blood flow to the white matter through therapies may be more successful than trying to get rid of the proteins. 

A simple treatment that may help is controlling high blood pressure, which can reduce the severity of white matter abnormalities.

White Matter and Traumatic Brain Injuries 

Patients with traumatic brain injuries (TBIs), particularly moderate and severe injuries, can be disabled for life. 

One of the most dangerous consequences of these injuries is chronic traumatic encephalopathy, a brain disease believed to cause progressive and irreversible dementia. 

In patients with TCL, accumulation of tau protein in the gray matter is evident. 

White matter lesions are frequently discovered in TBI survivors, according to researchers who have known this for a long time. Observations of the brains of people with repetitive TCLs - such as football players and military veterans, who have been studied frequently - have shown that damage to the white matter is evident and may precede the appearance of protein tangles in the gray matter. 

There is growing enthusiasm among scientists about the recent interest in white matter. Researchers are beginning to recognize that the traditional focus on studying gray matter has not yielded the expected results.

Learning more about the half of the brain known as the white matter could help us find the answers needed to ease the suffering of millions of people in the coming years.


 It is referred to as grey matter or grey matter to the component that makes up specific regions of the central nervous system (brain and spinal cord) that have a distinctive grey colour and are made up of glial cells, also known as neuroglia, as well as neuronal bodies (the "body" of neurons) and dendrites without myelin. 

The gray matter is found inside the spinal cord, tending towards the center and to the sides, in the shape of the letter H; and in the brain, on the other hand, in the external zone except in the basal ganglia, thus forming the cerebral cortex: the most complex nervous structure in the human body. 

In principle, as it is not covered with myelin, gray matter is not used for the rapid transmission of nerve impulses , which is why it is associated with other intellectual capacities of human beings , although it is not possible to state that a greater mass. of gray matter is to have greater intelligence, just as dolphins have more than human beings.

Gray Matter's Function

The brain's gray matter fulfills the vital function of being a receiver of information and in charge of thinking, that is, reasoning and memory in its various areas and meanings. From linguistic ability, perception, interpretation, abstraction and a huge etc. of mental and cognitive functions, they all depend on gray matter and the connections between its various types of neurons. 

On the other hand, in the spine, the gray matter acts as a regulator and selector of the information that will be transmitted to the brain , but also as a source of immediate impulses and the so-called “body memory” that allows all reactions not to have to come from the brain, which makes the work of nervous processing lighter.

Location of Gray Matter 

Gray matter is found all over the surface of the brain, as it forms the cerebral cortex, the most developed, complex and most connected area of ​​our entire nervous system. It is also found in the basal ganglia, deep in the cerebellum, and in the thalamus and hypothalamus areas. 

In turn, it can be found inside the spinal cord, in an H-shaped or butterfly-shaped segment, in the dorsal, intermediolateral and ventral horns of the vertebral column, as well as in the intermediate zone (dorsal nucleus of Clarke).

Importance of Gray Matter

Medical cases of people injured in regions of the brain rich in gray matter have been looked at, and the impact that such injuries can and often do have on several areas of human cognitive functioning has been observed: language ability, short-term or long-term memory. , associative capacity, learning , etc. 

As a result, it is now known that grey matter is the specific area of the nervous system that allows for the development of sophisticated, imaginative, and abstract thought in early humans. Therefore, not enough to have a larger brain volume to possess human intelligence, but it required a brain with an abundance of gray matter and a rough shell, which fosters countless connections between the neurons that compose it.

Gray Matter and White Matter 

Gray matter differs from white matter in much more than its color, determined by the high presence of myelin-bearing dendrites in the latter (myelin is whitish in color). They are distinguished in the speed of transmission of nerve information, much faster in the white matter than in the gray, and in the depth to which it is found, since the white matter is the interior of the brain (aunque the cover of the brain). spinal cord). 

For a long time it was thought that the white matter was passive, but today we know that it plays a vital role in the distribution of nerve information and in the modulation of action potentials, that is, it is responsible for the basic operational functions that it supports. complex processing, which is handled by gray matter, especially in the brain.

Difference between the Gray Matter and the White Matter of the brain

Chances are, you've come across terms like brain gray matter and white matter somewhere—like a study or a news article. However, the difference between the two is not always clear. After all, what are they for? What are the main features? 

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Basically, the gray matter and the white matter of the brain make up the central nervous system, which acts directly in perception, in the functioning of the body and in the performance of essential activities, such as locomotion, reasoning and memory.

The human nervous system, as a product of its phylogenetic evolution, is a very sophisticated system that has allowed, and still allows, us to relate, adapt to the environment and our survival. Several important functions depend on it, such as breathing, physiological activation when danger appears, cognitive functions (such as attention or memory), among others. 

The complexity of this system makes it still a great unknown for science. The nervous system has been the subject of study over the years and, although there are still many questions to be answered about it, we have a certain amount of knowledge about its functioning and structure.