Excerpt from The Man Who Wasn't There by Anil Ananthaswamy, plus links to reviews, author biography & more

It was a rather specific belief. And one that led Zeman to have some very strange conversations. "Look, Graham, you are able to hear me, see me, and understand what I'm saying, remember your past, and express yourself, surely your brain must be working," Zeman would say to Graham.

Graham would say, "No, no, my brain's dead. My mind is alive but my brain is dead."

Worse yet, Graham was distraught at his unsuccessful attempt at suicide. "He was one of the undead or half-dead," Zeman told me. "He in fact went and spent quite a bit of his time, for a while, in graveyards, because he felt he was with his own when he was there."

Zeman quizzed Graham to understand the grounds for this belief. It became clear that something very fundamental had shifted. Graham's subjective experience of himself and his world had changed. He no longer felt he needed to eat or drink. Things that once used to give him pleasure no longer did. "When he pulled on a cigarette, nothing happened," Zeman told me. Graham claimed that he never needed to sleep, that he did not feel sleepy. Of course, he was doing all of these things—eating, drinking, sleeping—but his desire for these and the intensity of his feelings had damped down dramatically.

Graham had lost something we all have: a keen sense of our own appetites and emotions. Patients suffering from depersonalization often report this emotional dulling or flatness. Depression too can bring about similar states of being, where emotions lose their edge. But these patients don't go on to develop such stark delusions of nonexistence. In Graham's case, the loss of emotional vividness was so extreme that "he had come to the conclusion, on the basis of that alteration in experience, that his brain must have died," said Zeman.

Zeman thinks that two key factors play a role in such robust delusions. One is a profound alteration in the quality of one's sense of oneself and the world—in Graham's case, the emotional rug had been pulled from under his feet. The second is an alteration in one's ability to reason about that experience. "Both things seemed to be true in Graham's case," said Zeman.

Graham's delusion was immune to evidence to the contrary. Zeman, in his conversations, would bring Graham to the point of surrender—to make him see the falseness of his delusion. Graham would acknowledge that a whole range of his mental faculties was intact, that he could see, hear, speak, think, remember, and so on.

So Zeman would say to him, "Clearly, Graham, your mind is alive."

He'd say, "Yeah, yeah, the mind is alive."

"The mind has a lot to do with the brain; surely your brain is alive," Zeman would prod him.

But Graham would not take the bait. "He'd say, 'No, my mind is alive, but my brain is dead. It died in that bath,'" Zeman told me. "You could get quite close to producing what you would think was knock-down evidence, but he wouldn't accept it." It was intriguing that Graham had developed such an explicit delusion—that of being dead because his brain was dead. Would his delusion have been different in an era when the legal definition of death did not include brain death?

Over the course of his medical practice, Zeman had only ever seen one other case of someone claiming to be dead. In the mid-1980s, working as a junior doctor in Bath, England, Zeman had to treat a woman who had undergone protracted bowel surgery and was suffering from severe malnourishment. Her body had been ravaged by repeated surgery. "She became very depressed as a result of that and formed a belief that she had died," Zeman said. "Which in a strange way seemed understandable to me, because the kind of trauma she was undergoing was so awful. She thought she was dead."

Zeman recognized the symptoms in Graham, and diagnosed him as suffering from Cotard's syndrome, which was first identified as a distinct disorder by the nineteenth-century French neurologist and psychiatrist Jules Cotard.

Excerpted from The Man Who Wasn't There by Anil Ananthaswamy. Copyright © 2015 by Anil Ananthaswamy. Excerpted by permission of Dutton. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.