A neurosurgeon claims to have been conscious and experienced heaven while the parts of his brain responsible for consciousness were offline: http://www.thedailybeast.com/newsweek/2012/10/07/proof-of-heaven-a-doctor-s-experience-with-the-afterlife.html
Heaven Is Real: A Doctor’s Experience With the Afterlife
When a neurosurgeon found himself in a coma, he experienced things he never thought possible—a journey to the afterlife.