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

For Cohen, Cotard's syndrome is revealing of the workings of the self. The disorder is a deeply felt disturbance of one's being, and shows that the self is linked to one's body, one's story, and one's social and cultural milieu. Brain, body, mind, self, and society are inextricably linked.

Back in Exeter, Adam Zeman had encountered something similar with Graham. The delusion in Graham's case was that his mind was alive but his brain was dead. "It was an updated, contemporary version of the Cotard's delusion. To come to the conclusion that your brain has died in isolation, . . . [you need] a concept of brain death, which is a relatively recent medical development."

What Zeman found even more intriguing was the inherent dualism in Graham's delusion—that an "immaterial" mind can exist independent of the brain and the body. "I thought it rather beautifully illustrated the dualism to which most of us are prone," Zeman told me. "The idea that your mind could be alive while your brain is dead is a rather extreme expression of dualism."

Philosophical musings aside, Zeman found Graham's situation sad. "He was slow and flat, with very little emotional modulation in his voice. [I] occasionally got a flicker of a smile, but there was rather little facial expression," said Zeman. "You had the sense of someone for whom existence was extremely bleak, and for whom thought was something of an effort."

A patient suffering from Cotard's syndrome is often extremely depressed. A depression far more serious than most of us can understand. I was given an insight into this by yet another French psychiatrist, William de Carvalho, whom I also met in Paris—at his office on avenue Victor-Hugo. He drew me a line diagram to illustrate where Cotard's stands on the depression scale. He started with "normal" on the left, then added "sad," "depressed," "very depressed," "melancholic" at equal intervals on the right. Then he added a series of dots—the progression was not linear anymore—and at the end of those dots he wrote, "Cotard's." "With Cotard's there is like a great black wall that goes from Earth to Saturn. You can't look over it," said de Carvalho, a dapper man of French-Senegalese descent with a way with words.

He had a private practice but also worked at the renowned Sainte Anne Hospital in Paris. He remembered one Cotard's patient that he treated in the early 1990s who showed classic signs of "melancholic omega." The phrase has its origins in Charles Darwin's descriptions of melancholia in his book The Expression of Emotions in Man and Animals: "a facial expression involving a wrinkling of the skin above the nose and between the eyebrows that resembles the Greek letter omega." While Darwin wrote about these "grief muscles" on the face, it was German psychiatrist Heinrich Schüle who coined the term "melancholic omega" in 1878, based on Darwin's vivid descriptions.

Dr. de Carvalho's patient was a fifty-year-old engineer and poet. The man had faked trying to kill his wife—he put his hands around her neck, then stopped, and told her to call the police. When the police came, they saw a very disturbed, even bizarre, man. So they took him directly to Sainte Anne Hospital rather than the police station (the man's act had a copycat quality to it: in 1980, the French philosopher Louis Althusser, who had been suffering from depression, strangled his wife, and was taken to a mental hospital first instead of being sent to jail).

The day after the incident, de Carvalho met the man at Sainte Anne Hospital. "I asked him, 'Why are you trying to kill your wife?' He said, 'Well, it's such a crime that I deserve to [have] my head cut.' He was hoping that he would be killed, even [though] there was no death penalty in France."

The man was exhibiting an extreme form of another symptom characteristic of Cotard's syndrome: guilt. "He told me at the time that he was worse than Hitler. And he asked us to help him to be killed, because he was so bad for humanity," said de Carvalho.

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.