As part of the central nervous system, gray matter is made from cell bodies, specifically the cell bodies of neurons, a neurophil, glial cells, and dendrites. Unlike white matter, this type of brain matter is found in areas of the brain that involve muscle control. It also is found among brain areas that control a person's perception, such as how things are seen or heard or the formation of memories. Speech and emotions are largely influenced by grey matter as well.
Gray matter is located in several areas of the brain. It can be found on the surfaces of the cerebral cortex and cerebellum. This type of matter is also found deep within the cerebrum. In the center of the spinal cord, both gray and white matter can be found, but gray is predominant.
The primary function of gray matter is to carry sensory information that comes from grey matter cells and sensory organs. This information is then passed to the areas of the brain that process sensory information. Intelligence and skill are often attributed to this brain matter, largely because it covers so much of the brain. Additionally, studies have shown that each person has different amounts and density of this brain matter, often showing higher concentrations in areas related to specific intellectual aspects or skill mastery.
Previous studies suggested that the size of a person's brain does not have any relation to intelligence levels. While larger sized brains were present in subjects with higher intelligence quotient (IQ) results, the increased IQ was not significant enough. More recent research has shown that IQ testing can activate multiple gray matter areas in the brain. This means that although a person may show strengths and weaknesses in specific areas of intelligence, both the strengths and weaknesses stem from a combined volume and activity level through the individual pattern of matter in the whole brain.
Although larger concentrations of gray matter can denote intelligence and skill, small concentrations and deficiencies can lead to problems. With elderly people, for example, studies have shown that short term memory is affected as the volume of grey matter decreases with aging. Studies have also shown that differences in grey matter volume may also be associated with certain psychological disorders, such as bipolar disorder. For some psychological disorders, evidence shows patients may have a grey matter deficiency in the region of the left parietal lobe. Severity and duration, however, are often determined by matter volume in the right frontal gyrus section of the brain.