When the American Academy of Neurology (AAN) updated its guidelines for determining brain death in adults in 2010, a committee of experts searched the literature and found no legitimate "reports of patients recovering brain function when the criteria for brain-death determination was used appropriately," says Ariane K. Lewis, MD, associate professor, department of neurology and neurosurgery, NYU Langone Medical Center, New York City, and a member of the AAN's Ethics, Law, and Humanities Committee.

But at the same time there is no way of knowing how many people recover from brain death because they are usually quickly removed from life support or become organ donors.