Gray Matter: Complete guide to how we process information


We “normal, everyday people” have all probably heard the term “gray matter” when talking about the brain. We’ve also probably heard about “white matter”. However this article is going to focus on what is gray matter, why is it called “gray”, and what is the difference between the two “colored” matters? What is it made of and what does its structure look like? What are some neat facts about the matter?

Gray Matter

Gray Matter

What is gray matter?

Gray matter, also spelled grey matter (British spelling) and also called substantia grisea, is the part of the brain that is controlled by the true dendrites (the short branching fibers that carry messages and impulses to the cell body) and nerve cell bodies (which bring information to the neurons). An easier definition is that it’s the unmyelinated neurons (a special coating for the nerve fibers) and other cells of the central nervous system. It is found in the brain, the brainstem, the cerebellum, and the spinal cord. Altogether, it makes up about 40% of the brain.

Gray matter is called that way because it’s actually gray… when it’s dead. Gray matter is gray due to the gray nuclei that make up the cells within it. However, when the brain is in a living person, the gray matter looks pinkish/brown due to the numerous tiny blood vessels that are known as capillaries that are there.

Males have an increased volume but a lower density of gray matter compared to females. Overall, our amount of gray matter develops, grows, and changes throughout our childhood and adolescence. However, around age eight, our volume of gray matter decreases, but later it begins to increase again once one ages into early adulthood.

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What is the difference between gray matter and white matter?

Our nervous system is divided into two parts: the peripheral nervous system and the central nervous system. Within the central nervous system, there is the brain and the spinal cord. The brain is divided into two categories: gray matter and white matter. While gray matter makes up about 40% of the brain, it takes up 94% of the brains’ oxygen. White matter makes up the other 60% of the brain.

Here are a few more differences between the two matters:

  • Gray matter has no myelin sheath, white matter is myelinated. Myelin is a lipid-rich material that surrounds the axon (nerve fibers) in some of the nerve cells. This myelin forms an electrically insulating coating. Myelin is essential for the nervous system to work well.
  • Gray matter is gray due to the gray nuclei that make up the cells within it. White matter, because it has myelin, appears white. However, when the brain is in a living person, the gray matter looks pinkish/brown due to the numerous tiny blood vessels are known as capillaries that are there.
  • Gray matter neurons don’t have extended axons while white matter neurons do. This means that white matter has nerve fibers that are longer and can go further throughout the body than gray matter nerve fibers.
  • Grey matter stops processing communication while white matter allows for the communication to pass to and from the gray matter areas, as well as between the gray areas to allow the communication to reach other parts of the body.
  • In the brain, gray matter is on the surface, known as the cortex. White matter is buried deep within the brain. In the spinal cord, it’s the opposite: gray matter is at the core of the cord while white matter is on the outside insulating.
  • Grey matter is made up of nerve cell bodies (little cells that bring information to neurons) while white matter is made up of fibers (the nerves).

The composition of gray matter

Gray matter is made up of glial cells and unmyelinated axons. Glial cells are cells that surround the neurons in the brain and try to support them as well as provide insulation between them. Types of glial cells include astrocytes, Schwann cells, ependymal cells, microglia, satellite cells, and oligodendrocytes. They are most often found in the central nervous system. To define “unmyelinated axons”, it’s best to first define “myelin”. Myelin is a lipid-rich (rich in fat) substance that surrounds the axon of some of the nerve cells in the brain. The myelin forms an insulating later and essential for the function of the nervous system. However, grey matter is unmyelinated– meaning it lacks this white-colored fatty protein myelin. Grey matter also contains neuronal cell bodies.

Structure of gray matter

Gray matter is found throughout the brain, the brainstem, the cerebellum, and the spinal cord. In the brain, it’s found at the cerebral cortex (the surface of the two cerebral hemispheres, between the left and right). It’s also found in the cerebellar cortex (the cerebellum) and within the depths of the cerebrum such as the thalamus, subthalamus, hypothalamus, and the basal ganglia. The basal ganglia includes the nucleus accumbens, globus pallidus, putamen, and the septal nuclei. Gray matter can also be found in the cerebellar which includes areas in the brain such as the globose nucleus, emboliform nucleus, dentate nucleus, and the fastigial nucleus. Within the brain, it’s also found at the very end in the brainstem. Within the brainstem, gray matter located in the olivary nuclei, red nucleus, substantia nigra, and the cranial nerve nuclei.

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Within the spinal cord, gray matter is called the gray column (gray column). It consists of interneurons and cell bodies of projection neurons. It travels downward from the top of the spinal cord t the bottom and is distributed into three gray columns that are shaped like an “H”. The first column is forward-facing and is known as the anterior gray column. The second column is rear-facing and is known as the posterior gray column. The third column interlinks and is known as the lateral gray column. The left side and right side gray matter is connected by the gray commissure– a thin strip of gray matter that surrounds the main canal of the spinal cord and that connects the two halves of the spinal cord using white commissure from white matter, as well.

What is the purpose of gray matter?

The whole purpose of gray matter is to process information in the brain. The structures that make up gray matter process the signals that are generated by the sensory organs (eyes, tongue, ears, nose, and skin) and other areas of the gray matter. The tissue then directs the sensory stimuli (motor stimuli) to the nerve cells within the central nervous system where the synapses produce a response to the stimuli. These signals reach the gray matter via the myelinated axons (the material that makes up white matter) in the cerebellum, cerebrum, and spine.

What happens when you have too much gray matter? Well, gray matter heterotopia happens. It’s a neurological disorder that is caused by clumps of gray matter that are located in the wrong part of the brain. The neurons within the gray clumps are normal, like all other gray matter, they are just in the wrong part of the brain. Gray matter heterotopia can cause epilepsy, mental retardation, a loss of motor skills, and/or a disability to function cognitively on higher levels. The severity can cause the symptoms to range from almost nothing to incredibly profound. Sometimes, someone is found to have grey matter heterotopia by having a brain scan for another condition and had no prior knowledge or symptoms of their misplaced grey matter.

Gray Matter

Gray Matter is made up of many neurons and fibers that run throughout the brain

Studies on gray matter

Too much multitasking can affect your gray matter. In one of the first studies ever that correlates a direct link between the physical structure of the brain and behavior, multimedia multitasking has its impact on our social-emotional well-being as well as our overall cognition. Ryota Kanai and Kep Kee Loh from the University of Sussex’s Sackler Center for Consciousness Science took a functional magnetic resonance imaging machine (fMRI) and they looked at the brain structure of 75 adults who had previously answered questions about their media use such as computers, cell phones, TV’s, and print media (newspapers). People who reported using more devices (a computer and a TV, rather than just a computer alone) had a lower grey matter density in their anterior cingulate cortex (ACC)– a part of the brain associated with emotional and cognitive processing.

Practicing mindfulness leads to an increase in regional brain gray matter density. This study looked at how therapeutic interventions that blended in mindfulness meditation worked with our neural mechanisms. Using Mindfulness-Based Stress Reduction (MBSR), one of the most widely used mindfulness training programs, the researchers took anatomical MRI images of 16 healthy, “meditation-naïve” people before and after finishing an eight-week program of MBSR. The results were compared to a group of 17 non-participants for a control group. The changes in their grey matter were significant. Those who participated in the eight-week-long mindfulness program had increased grey matter in their left hippocampus, the cerebellum, the temporoparietal junction, and the posterior cingulate cortex- all parts of the brain associated with concentration, learning, memory, perspective taking, self-referential processing, and emotional regulation.

Gray matter has been associated with language processing for people with a family history of dyslexia. An Italian research team took 10 people with familial dyslexia (at least one close relative with clinically evident dyslexia or a long history of reading issues) and 11 people to have as a control group. They employed the voxel-based morphometry (VBM) method which allowed for a more in-depth look at and measurement of gray-white tissue volume and density compared to other tools that measure grey matter. The study was the first study ever to take into account the whole brain volume, age of the participants, and the differences in brain shape. The study found that there were grey matter abnormalities in many parts of the brain that are important and essential for language functions such as the right middle temporal gyrus, the left superior gyrus, the inferior temporal gyrus, cerebellar nuclei, the planum temporale, and the inferior temporal cortex.

Cortical gray matter loss in treatment-naïve and alcohol-dependent people. Most studies examine the impact of alcohol dependence on people who are already undergoing treatment- but not this study! The study found that there are cortical (the outer layer of the cerebellum) grey matter volume reductions- mostly in the parietal and prefrontal regions of the brain- in heavy drinkers (male). The volume loss wasn’t tied with a family history of alcoholism nor with education which means that the loss is a direct effect of alcohol ingestion. The study found no difference in volume for white matter nor temporal lobe volume loss.

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Reduced gray matter volume found in normal adults with a (maternal) family history of Alzheimer’s disease. The study, on behalf of the Kansas University Brain Aging Project, took 67 cognitively healthy people with a maternal history of late-onset Alzheimer’s, a paternal history of Alzheimer’s, or no parental history of Alzheimer’s who were all similar in age, gender, education, and Mini-Mental State Examination scores. It was found that people, although they are cognitively healthy themselves, who have a family history of late-onset Alzheimer’s disease had significantly lower gray matter volume in the middle frontal lobe, the inferior frontal lobe, the precuneus, and the superior frontal gyri compared to those who had no parental history of Alzheimer’s. Those who had a paternal history of Alzheimer’s were found to have noticeably smaller middle frontal lobe, inferior frontal lobe, precuneus, and lingual gyri.

As an older adult, playing Super Mario 64 (in 3-D) might increase your gray matter in the hippocampus. The fun study found that people who played 3D video games can have an increased growth in the cerebellum and hippocampus.

Weird facts about gray matter

  • Those who have a larger amount of grey matter might perform better on language tasks.
  • Although men have a less overall grey matter in their brains than women do, they have more cerebrospinal fluid and white matter than women.
  • Regular exercise might lead to an increased amount of gray matter inside the hippocampus.
  • It’s important during physical activities because it helps you think and move at the same time.
  • Even though grey matter only makes up 40% of the brain, it is in control of our muscles, memory, and speech!

Using your gray matter, let us know what you think in the comments below!

Anna is a freelance writer who is passionate about translation, psychology, and how the world works.