However, a University of Cork professor suggests a more scientific reason for the phenomenon. Writing in the Irish Times, Emeritus Professor of Biochemistry William Reville argued that NDEs probably reflect the activity of the dying brain as oxygen levels fall and carbon dioxide levels rise. He said: "NDE reports of light at the end of a dark tunnel could simply reflect oxygen levels falling in the retina, starting at the periphery and moving inwards towards the centre, producing tunnel vision." NDE is commonly experienced by people who have suffered an extreme medical trauma (Image: Getty) Patients who have experienced an NDE often recall seeing bright light at the end of a tunnel (Image: Getty)