We cannot know how to fix a problem until we understand its causes. But even for some of the most common mental health problems, three specialists might offer you three completely different treatments.

As a cognitive neuropsychiatrist, Professor Anthony David brings together many fields of study, from social and cognitive psychology to neurology. The key for each patient might be anything from a traumatic memory to a chemical imbalance, an unhealthy way of thinking or a hidden tumour.

Patrick believes he is dead; Jennifer's schizophrenia medication seems to bring on the symptoms of Parkinson's; Emma is in a coma – or is she just refusing to respond?

These are the fascinating case studies that have driven the most startling insights in Anthony's forty-year career studying illnesses at the edge of human understanding.