Draaisma argues that delusions are the result of the self’s ingenuity in maintaining inner order in the midst of chaos. Delusions form a mosaic in which certain patterns can be recognized. Some are linked to brain damage and help understand the neurological circuits that must remain intact to ensure mental balance. Others are an attempt to put confusing sensations into an intelligible context. For example, Draaisma offers an account of a watchmaker who becomes convinced he has lost his head – during decapitation’s heyday. The man acknowledges there is a head on his body, but it is an inferior one, taken from the guillotine’s pile. Delusions, Draaisma argues, are linked to time and place.

There is an internal logic to delusions, take Cotard syndrome, whose sufferers are convinced they have died. Patients are aware they are still walking around and talking to others, yet they remain convinced they are dead and don’t eat. One possible explanation is the body’s representation in the brain. Specific body parts are linked to sites in the cerebral cortex. If one’s entire bodily representation is disrupted, then the whole body feels foreign. It is the opposite of the phantom limb sensations to which Draaisma devotes another fascinating chapter. Draaisma discusses the thousands of war veterans who experience this.

Sufferers of Capgras syndrome believe that a loved one has been replaced by a double. Unfortu­nately, these patients can never be freed from their delusion. Rather, the opposite happens: the doctor is soon perceived as being part of the conspiracy. Other chapters cover a dubious psychological experiment with three delusional Christs in a Michigan psychiatric facility, and people desperate to rid themselves of a limb. Draaisma concludes his book with a chapter on grief-induced hallucinations, which are surprisingly common, though only a minority reports them for fear of being declared insane.

This entertaining book is relatively short, but it contains a wealth of information and fascinating insights. Draaisma is a compelling storyteller and always instructive.