The Cotard delusion, also known as the Walking Corpse Syndrome, is a rare mental disorder that convinces people that they're walking, rotting corpses with missing organs.

The Cotard delusion is a rare mental illness that causes a person to believe that they are dead. This could mean they think they've died and are still somehow walking around; it could mean they think vital organs such a their heart of liver is missing or putrefying within them; or it could mean something more philosophical, that they believe they no longer exist, despite any evidence to the contrary.

A 1995 study published in the journal Acta Psychiatrica Scandinavica and conducted on 100 cases of Cotard delusion found that 69 percent of the patients held the belief that they didn't actually exist, and yet, curiously, 55 percent of this group also held the delusion that they were immortal.

The disorder was named by French neurologist Jules Cotard in 1880. That year, he had been visited by a woman who was under the delusion that she had no brain, no nerves, no stomach, and no intestines. She believed that, however unlikely the science behind it, she was a walking, talking, rotting corpse. Cotard reported that she had no belief in God or the afterlife, and didn't feel any need to eat, so ended up dying of starvation. 

Interestingly, the disorder was actually first reported almost a century earlier, by French naturalist and philosophical writer Charles Bonnet. Bonnet became aware of a woman who had suffered from a blow to the neck, which paralysed her on one side as if she'd had a stroke. Upon recovering her speech, it became apparent to all those around her that she believed herself to be dead.

Reporting in a 1788 edition of the British Journal of Psychiatry, Bonnet described the woman's actions:

[T]he 'dead woman' became agitated and began to scold her friends vigorously for their negligence in not offering her this last service; and as they hesitated even longer, she became extremely impatient, and began to press her maid with threats to dress her as a dead person. Eventually everybody thought it was necessary to dress her like a corpse and to lay her out in order to calm her down. The old lady tried to make herself look as neat as possible, rearranging tucks and pins, inspecting the seam of her shroud, and was expressing dissatisfaction with the whiteness of her linen. In the end she fell asleep, and was then undressed and put into bed.

Bonnet prescribed a treatment of opium to the woman to calm her down. According to the Chirurgeon's Apprentice blog, she eventually grew out of the delusion somewhat, but it would come back every three months or so, when she believed she was dead and communing with other dead people.

More recently, Helen Thomson from New Scientist interviewed a man named Graham, who described his experience living with the disorder:

"When I was in hospital I kept on telling them that the tablets weren't going to do me any good 'cause my brain was dead. I lost my sense of smell and taste. I didn't need to eat, or speak, or do anything. I ended up spending time in the graveyard because that was the closest I could get to death."

The Cotard delusion is thought to be caused by neurons misfiring in the fusiform gyrus region of the brain, which is related to our ability to recognise different faces, and the amygdala, which allows us to associate emotions with a face we've recognised. Due to the disruption of these mental abilities, a patient can suffer from derealisation, which is a wider disorder that causes an all-consuming feeling of disconnection from one's environment, and if they cannot recognise their own face on top of that, or associate any emotions with it, it can result in the Cotard delusion. 

A person is more likely to develop the Cotard delusion if they also suffer from some kind of psychosis, such as schizophrenia, or another neurological or mental illness that enhances the feeling of disconnection. Treatment is usually administered in the form of using antidepressant, antipsychotic, and mood stabilising drugs, or electroconvulsive therapy (ECT) if the patient is showing signs of clinical depression.

Sources: The Chirurgeon's ApprenticeNew Scientist