An injury to the brain can be devastating. When brain cells die, whether from head trauma, stroke or disease, a substance called glutamate floods the surrounding areas, overloading the cells in its path and setting off a chain reaction that damages whole swathes of tissue. Glutamate is always present in the brain, where it carries nerve impulses across the gaps between cells. But when this chemical is released by damaged or dying brain cells, the result is a flood that overexcites nearby cells and kills them. >>> Discuss This Story