The invention provides a cerebral nitric oxide donor for use in a method for assessing the extent of brain dysfunction following brain injury, said method comprising contacting at least a portion of the brain of a subject with a brain injury with said cerebral nitric oxide donor and determining whether or not there is a subsequent change in one or more aspects of brain physiology, wherein the extent by which said one or more aspects of brain physiology improves is indicative of the extent of brain dysfunction.