杏吧原创

Your latest novel is about a man who is possessed. Did any of your patients have that belief?
Once a patient came in and said: 鈥淚 am possessed by a demon.鈥� This guy wasn鈥檛 insane, he wasn鈥檛 schizophrenic 鈥� he just had this particular belief. In my day we called it 鈥渕onosymptomatic delusion鈥�, but now it would be called something like 鈥渄elusional disorder鈥�. That鈥檚 when you鈥檙e completely sound and reasonable in every respect except you have one belief that is absolutely bonkers.

Why would an otherwise well person believe something like that?
He was misattributing certain symptoms he had to a demonic presence. When you鈥檙e possessed, you鈥檙e supposed to get headaches, and he was getting loads of headaches.

I can鈥檛 imagine making that assumption myself鈥�
You have to have an openness to it. Lots of people are open to all kinds of spiritual and magical beliefs. An individual could have a perfectly harmless interest in the supernatural but then something happens that triggers this delusion and they get stuck with it, reinforcing it by piling up one misinterpretation after another. If you go out looking for evidence, you will find it.

What kind of evidence?
In my patient鈥檚 case, he wanted to know the demon鈥檚 name, so he got a Ouija board out. This shows he had a willingness to go down a particular path. When you think about the way that brains work, our natural inclination is to look for causes.

Could anyone end up with delusions like these?
Theoretically, yes, in the right circumstances. Maybe we all get such episodes in our lives. It鈥檚 not that unusual for people to think they are seriously ill without much evidence. Who hasn鈥檛 had a health scare for no good reason? That鈥檚 taking a symptom and extrapolating, then finding more evidence that supports the belief.

Are there any other examples?
The big one is people suspecting that their spouse is cheating on them. Morbid obsessions about infidelity are relatively common and produce spectacular behaviours, often in individuals who otherwise are OK. In a way, falling in love is kind of monosymptomatic delusion. Even though you鈥檙e a rational person, you can engage in all kinds of irrational behaviour because you are fixated on a particular individual.

Can these delusions be treated?
In the past they were treated with lots of medication or were perceived as untreatable. But these days, not just monosymptomatic delusions but all forms of psychotic illness are increasingly treated with cognitive behavioural therapy. You cultivate a sort of scientific attitude in the patient, getting them to test their beliefs. It is probably the most important new advance in psychotherapy.