A common image of the human brain is a uniform, dull gray mass, often seen in textbooks and media. This popular perception, however, is inaccurate when describing the organ in a living body. A functional, oxygenated brain exhibits varying shades of pink and reddish-brown, a direct result of its intense metabolic activity. The familiar gray color only appears after the tissue has been removed and treated.
The Vivid Color of the Living Brain
The living brain’s pinkish-red hue is a direct consequence of its immense circulatory demands. Although the brain constitutes only about two percent of the body’s mass, it consumes roughly 20 percent of the body’s total oxygen and blood supply. This high requirement is met by an extensive network of blood vessels, including tiny capillaries that permeate the tissue.
The color comes from oxygenated blood circulating through these vessels. Hemoglobin, the iron-rich protein within red blood cells, gives blood its bright red color, causing the densely packed organ to take on a reddish-pink appearance while circulation is active.
Distinguishing Gray Matter from White Matter
The overall pink color of the living brain is not uniform, as the two primary tissue types, gray matter and white matter, differ in appearance. Gray matter refers to areas rich in neuronal cell bodies, dendrites, glial cells, and capillaries. When blood flow is present, this tissue appears light gray with pinkish or tan tones due to the high density of cells and blood vessels.
White matter is composed mainly of bundles of axons that connect different brain regions. These axons are wrapped in the myelin sheath, a protective layer made of proteins and lipids, whose high content gives the white matter a lighter, almost white or creamy color that contrasts with the darker gray matter.
Why Brains Are Often Portrayed as Gray
The misconception that the brain is gray originates from the appearance of post-mortem specimens used for study. After death, the blood that gives the tissue its living pink color is no longer circulating and is drained away. This immediate loss of blood dulls the overall coloration.
Furthermore, brain tissue is typically treated with chemical fixatives, such as formalin, for long-term preservation. This chemical process stops decomposition, hardens the tissue, and chemically alters the remaining components, resulting in a uniform, muted beige or dull gray color.