The interview - Capgras Delusion

You have both worked for manyyears on a number of problems that people face following neurological insult, but today I want to focus purely on the rather strange syndrome known as 'Capgras delusion'. What does it involve? 

AY People who claim that their relatives are robots, duplicates or impostors.  

KdP It's not restricted to relatives – it may also pertain to acquaintances or close friends, and sometimes inanimate objects are regarded as changed or not the real thing. Even locations may be perceived as fake duplicates – a whole district or town may be regarded as false and reconstructed.

AY Obviously it causes people's relatives enormous distress – to be sitting over the breakfast table with your husband telling you you're an impostor. It also presents the significant risk that the people who have this delusion will be violent towards the impostors – so it's a worrying condition.

That sounds extraordinary! Can you give me any examples of case studies to help illustrate how it affects people? 

KdP I think the most dramatic one that's recorded in the literature is of a young American man who developed the belief that his father wasn't a real person and had been duplicated. He actually believed that he was a robot – a kind of 'humanoid'. At the height of his suspicion he decapitated his father and took the head to the authorities and demanded it be examined for electronic devices to prove his point. Of course, in most cases the outcome is not as unfortunate as this, it's more about believing there are very subtle differences in someone's facial appearance. They say things like, 'Well of course he looks like so-and-so but he's slightly thinner, or he's fatter, or his hair colour is subtly different and I can see that you obviously don't know the person as well as I do.' They seem to be very particular about minute details to prove their point.

Another case, the first we ever saw, was a lady in her early sixties who had suffered a stroke. She fully recovered from the stroke but within a year she started to believe that a cousin of hers and his lady friend were following her in disguise. But she was able to see through their clever disguises, while anybody else would have seen them as complete strangers. She claimed they were following her around because they knew that she was aware of certain illegal activities of the cousin.
Not very pleasant for the relatives.

So it can be as disturbing for the relatives and loved ones of the sufferer as for the sufferer themselves. Do any of them ever gain any insight into their problems?

KdP It depends very much on the clinical setting in which these patients present. There is a wide variety of neuropsychiatric conditions in which these delusions may occur, e.g. traumatic brain injury or a toxic state or a pre-existing psychiatric disorder. It depends very much on how treatable the underlying illness is. You get a range of responses, from a complete resolution, or no response, to a partial response where the person still has some belief that something strange has been going on but it's no longer bothersome and they've somehow learnt to live with it.

AY I have the feeling that some of the patients that we saw reached a point where they realise that going on about this just attracts too much attention to themselves, so they stop.

Although they may not develop complete insight – they realise there is at least a problem, and that others are responding badly to them?

AY Yes. One of the extraordinary things is that they realise that other people are going to find this claim completely unbelievable. If you say to them, 'What would you think if I said to you, "I think my wife's an impostor",' they'd say, 'You're barking mad.' However, they also say, 'But this really has happened to me.' There is something that's encapsulated about the delusion. They understand perfectly well that anyone else is going to find this claim incredible. It's rather like if you think you've seen a ghost, there's no point me saying it was reflections or photons in your eye and things like that. It's your experience and you will listen politely while I tell you all of that, and then say, 'Yeah, but I saw it – you didn't.'

Can we tie this down to specific areas of the brain that are damaged? 

AY It's not easy. As Karel said, the aetiologies are very variable. When it does follow brain damage there are usually pretty widespread lesions. The lesions nearly always encompass parts of the frontal lobes and that obviously is a clue. They often are also close to regions that would have been damaged in prosopagnosia, where people have a general problem with face recognition. I think it was that which got Hadyn Ellis and me interested in this delusion in the first place.

You both worked with Hadyn sometime ago on Capgras – how did this come about?

KdP It was actually due to my wife, who is also a consultant psychiatrist. She approached him after he'd given a talk on prosopagnosia and facial recognition tests. And she said to him, 'What sort of test would you suggest in a case like Capgras?' He got very interested – it all stemmed from that first contact.

AY By that time people had noticed that the brain lesions associated with Capgras delusion were rather like the brain lesions linked to prosopagnosia. So there was a lot of interest in the idea that Capgras delusion is somehow a variant of prosopagnosia, and at the time the best theory we had about prosopagnosia was that it's a disorder of overt recognition. That is being unable to say, 'That is my wife, that is my father, that is Adolf Hitler,' etc., etc. Whereas certain forms of implicit response, emotional responses and so on, as measured by things like skin conductance, are relatively preserved in prosopagnosia – people don't overtly show recognition but they do implicitly. The insight that Hadyn had was that maybe Capgras delusion was not an equivalent of prosopagnosia, but instead the exact mirror image of it. In other words, the emotional responses had gone but the overt recognition is still there, so you see your wife but she doesn't feel like your wife.

You recognise the nose, the eyes and everything – but the gut feeling's gone?

AY Yes. When we tested patients with Capgras delusion we found that they do recognise familiar faces reasonably well. You can give them a whole load of famous faces and say, 'Who are these?', and their score is pretty much the same as yours or mine would be. But they show no skin conductance response to faces at all. So we thought that's fairly convincing evidence for this theory – since we had produced a falsifiable prediction that was borne out.

What can you do about it, Karel? How can you treat it?

KdP I think it largely depends on the clinical context in which these patients present. In the main the vast majority suffer from a primary psychotic illness, e.g. schizophrenia, or a severe mood disorder and are treated with an anti-psychotic agent. Where the delusion arises secondary to an underlying medical condition, such as a brain tumour or some kind of metabolic disturbance, they are treated according to the nature of the particular illness, but in some cases they may also require an anti-psychotic agent, such as with the lady already mentioned who had suffered a stroke.  

AY I think it's important to point out that our original idea that Capgras delusion is in a sense a mirror image of prosopagnosia was developed further over a period of almost 15 years working with Karel and Hadyn. We gradually realised that although this is the core of the deficit, there are a lot of other contributory factors. In the end we came to the conclusion that what causes this delusion is a very unfortunate interaction of a number of different deficits. For example, a patient may have a brain injury or for some reason their emotional responses to the things they see are diminished, and this leads them to the suspicion that things are changing. When you're in a suspicious mood you very often mistake changes in yourself for changes in the outside world. They begin to think the changes are in the outside world, and they then accuse their wife or their mother, or whoever, over the breakfast table of being an impostor. Their mother or their wife then starts behaving strangely towards them. This confirms in them the idea that it is an impostor, and the whole thing spirals out of control.

So it is our firm view that it's not a single impairment. It's a whole constellation of things, and the implication is that if you tackle any one of those problems you can probably diminish the overall pattern to the point where it becomes possible to do something about it. I think that's where Karel is coming from. It's not really a direct treatment of the delusion so much as chipping away at the various factors which are creating it, in the hope that once one of them is removed the rest can go.

Karel mentioned schizophrenia – does it overlap with Capgras? 

KdP It's not that it is a form of schizophrenia – you can have Capgras without schizophrenia and most patients with schizophrenia never develop this delusion. But in a large number of cases, patients have been diagnosed on other criteria as suffering from schizophrenia and then developed this as perhaps one of many other delusions they may have. But there are occasions when you don't have a previous history of any clinical abnormality where it might suddenly arise, e.g. in elderly or middle-aged people clinicians always have to rule out that they have not suffered some subtle brain injury like a stroke. In these cases the clinical picture can be quite different from schizophrenia.
And do these clinical pictures, particularly the extreme examples, help us to understand Capgras delusion?

AY Sometimes they just add to the mystery. There are cases where people with Capgras shift their delusion from believing their relatives are impostors to saying, 'I myself am a dead person'… completely bizarre. How can you be sitting there saying, 'I'm talking to you but actually I've died.'

KdP We saw one or two cases ourselves of people who had actually fluctuated between these two, apparently extraordinarily rare delusions.

AY And this shift seems to happens when their mood changes. When they're in a very suspicious mood they think that all the perceptual changes that have happened to them are a consequence of something going on in the outside world. They say, 'These people are impostors – everything's fake.' But when they become very depressed about their condition they think that all the changes that have happened are due to something catastrophic that has happened inside them. They arrive at the belief that, 'I'm a dead person – things could not be so different unless I'd died.' I think that what is interesting about what we've been doing is that it allows you to conceptualise why these different delusions should go together. You can see a person actually change their delusional belief according to changes in their circumstances… changes in their mood particularly.