The wonders of the human mind are perhaps most evident in what it does when you are not thinking.

When you want to move your arm it just moves. You remember the things you experience. And when you look at the incredibly complex world in which you live it intuitively makes sense to you.

But what happens if even one of these innate faculties fails?

Anthony David is Director of University College London’s Institute of Mental Health and author of Into The Abyss: A Neuropsychiatrist’s Notes on Troubled Minds