Details, from The Telegraph:
Near death experiences in which people report “seeing the light” could be explained by increases in electrical activity in the brain after the heart stops, scientists have found. The first study to examine the neurophysiological state of the dying brain in animals has identified surges in activity, which suggest a level of consciousness after “clinical death” – when the heart stops beating and blood stops flowing to the brain. Researchers analyzed the recordings of brain activity using electroencephalograms (EEGs) from nine anesthetized rats undergoing experimentally induced cardiac arrest. Within the first 30 seconds after cardiac arrest, all of the rats displayed a widespread, transient surge of highly synchronized brain activity that had features associated with a highly aroused and conscious brain. Almost identical patterns were found in the dying brains of rats undergoing asphyxiation, according to the research by the University of Michigan, published in the Proceedings of the National Academy of Sciences. Whether and how the dying brain is capable of generating conscious activity has been vigorously debated. Approximately 20 percent of cardiac arrest survivors report having had a near-death experience during clinical death.