And now, a brain scientist trained at harvard is saying something that's challenging his scientific world tonight. He says that he has been to heaven. He can prove it. And he's returned with a message... See More
And now, a brain scientist trained at harvard is saying something that's challenging his scientific world tonight. He says that he has been to heaven. He can prove it. And he's returned with a message for us all. "Nightline" anchor terry moran tells us his story. Reporter: At the alexander home in lynchburg, virginia -- grace is different now. Eban alexander is a harvard neurosurgeon and brain scientist who nearly died four years ago when a ferocious e. Coli meningitis infection attacked his brain and plunged him deep into a coma for a week. Brain scans showed that all of the parts of his brain that make us human, that give us consciousness, thought, memory and understanding -- was not functioning. They should be a very rich network of them. Reporter: Right. Yet, we don't really see that because they're all filled with Reporter: Doctors gave him up for dead, but after a week, eban alexander awoke, he says, with a wondrous memory. Did you go to heaven? Yes. I was rescued by this beautiful spinning white light that had a melody, and incredibly beautiful melody with it that opened up into a bright valley. Reporter: God was there, he says, as a vast presence of love. And eban says there was a young woman who soared across heaven with him on a butterfly wing, and who gave him a message to take back from heaven. "You are loved. You are cherished. There's nothing you have to fear. There's nothing you can do wrong." Reporter: And that woman, after he recovered, he saw a picture of his long, dead sister that he never met, it was her. It was the most profound experience I've ever had in this life. Reporter: A lot of people are going to say, "doctor, it was a hallucination." I know this is not a hallucination. It really occurred, and it occurred outside of my brain. Reporter: Many of his colleagues in neuroscience are deeply skeptical, saying his brain must have produced these visions, perhaps ae out of the coma. But he said it's incompatible. Our soul, our consciousness, our spirit, doesn't depend on the existence of the brain and body at all. Reporter: After he came out of his coma before he talked to anyone else, eban alexander wrote down everything that he could remember, 20,000 words. He described in detail that young woman on that butterfly wing, not until he saw the picture of his dead sister, he says, it was her. So, are a lot of colleagues contending him, challenging him on the science? A lot of his colleagues are challenging him on the science. He invites it. Let's have a discussion. So much to fascinate us. Terry will have a lot more of his reporting tonight on "nightline."
This transcript has been automatically generated and may not be 100% accurate.