- Gray matter is one of the two major types of nervous tissue found in the central nervous system (CNS), the other being white matter. It is named for its grayish-pink color, which is due to the absence of myelin (a fatty white substance that insulates axons), and the high density of neuronal cell bodies, dendrites, unmyelinated axons, glial cells (such as astrocytes and oligodendrocytes), and capillaries.
- Gray matter is crucial for processing information in the brain and spinal cord and plays a central role in muscle control, sensory perception, memory, emotions, decision-making, and self-control.
- In the brain, gray matter is primarily located in the cerebral cortex—the outer layer of the cerebrum—and in subcortical structures such as the basal ganglia, thalamus, hypothalamus, and limbic system (including the amygdala and hippocampus). The cerebellar cortex, covering the cerebellum, is also made up of gray matter. These regions are responsible for a wide range of higher-order brain functions, including conscious thought, voluntary movement, language, and emotion. The density and organization of gray matter in the cerebral cortex, particularly in areas like the prefrontal cortex, are closely associated with cognitive ability and intelligence.
- In the spinal cord, gray matter forms an H-shaped or butterfly-shaped structure in the center, surrounded by white matter. It consists of the anterior (ventral) horns, which contain motor neurons that control skeletal muscles; the posterior (dorsal) horns, which receive sensory input from the body; and the lateral horns, present only in certain segments, involved in autonomic motor functions. The spinal gray matter integrates and relays motor and sensory signals and serves as the first site of reflex arc processing.
- Gray matter is essential for synaptic communication between neurons. Its abundance of dendrites and synapses makes it the primary site where information is received, interpreted, and integrated. In contrast, white matter primarily facilitates the transmission of signals between different gray matter areas and between gray matter and the rest of the body.
- Throughout life, the volume and distribution of gray matter can change, a process influenced by development, learning, aging, and disease. During childhood and adolescence, gray matter increases in volume and then undergoes synaptic pruning, where unnecessary neuronal connections are eliminated to improve neural efficiency. This maturation process is critical for the development of cognitive and behavioral control. With aging, gray matter typically decreases in volume, especially in the frontal and temporal lobes, which may relate to age-associated declines in memory and executive function.
- Abnormalities in gray matter structure or volume are associated with numerous neurological and psychiatric disorders. For example, reduced gray matter has been observed in Alzheimer’s disease, schizophrenia, major depressive disorder, and autism spectrum disorders. These changes can reflect neuronal loss, atrophy, or altered synaptic activity. Imaging techniques such as magnetic resonance imaging (MRI) are commonly used to study gray matter volume and distribution in both healthy and diseased brains.
