Credit: Columbia Engineering
The blush of the brain. Red hue shows the increase in the amount of blood in the brain (total hemoglobin concentration) in response to stimulation. This response extends up along surface arteries in a wave of dilation that travels over a millimeter in less than half a second. This ‘brain blush’ provides the contrast seen in fMRI images, and is essential for normal brain function. The green vessel crossing the responding region is a draining vein. Veins exhibit very little diameter change in response to normal stimulation, acting as passive drains of increased blood flow.