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Body doubles and alien replicants: Capgras delusions explained

In the film Invasion of the Body Snatchers aliens invade earth by replicating individuals. While the idea that we could be duped by shape-shifting aliens is a great idea for a film, the story echoes a…

Hi Mum … or should I say … impostor? Aaron Tait/Flickr, CC BY-SA

In the film Invasion of the Body Snatchers aliens invade earth by replicating individuals. While the idea that we could be duped by shape-shifting aliens is a great idea for a film, the story echoes a bizarre appeal playing out around Senate elections in the United States.

Senate candidate Timothy Ray Murray has reported that he believes that his political opponent, Senator Frank Lucas, is dead and being impersonated by a body double.

Actually, in what initially seems more like a pitch for an episode of the TV series Get Smart than an alien invasion, Candidate Murray claimed that Senator Lucas died in 2007. He was then replaced by a body double.

Subsequently – Murray claims – that body double was hanged in the Ukraine in 2011 before being replaced by a body double double.

While it is tempting to think that Candidate Murray may be on to something – the idea that governments are populated by emotionless aliens carries considerable intuitive appeal – it is more likely that Candidate Murray may be suffering a Capgras delusion.

Capgras delusions

Described first in 1923 by French psychiatrist Joseph Capgras and his colleague Jean Reboul-Lachaux, Capgras delusions are characterised by the belief that someone known to us – a friend, spouse, child, parent or whomever – has been replaced by a physically identical impostor.

‘Jamaican me out to be some kind of alien …’ Ricardo Liberato/Flickr, CC BY

If that sounds familiar, or if a dearly loved elder has accused you of not being whom you claim to be, it is because these types of delusions are not uncommon.

Indeed, Capgras delusions are part of a larger group of misperceptions known as delusional misidentification syndrome.

More common in females than males by a ratio of three to two, Capgras delusions can occur in patients with paranoid schizophrenia or with neurodegenerative diseases, including dementia.

They can arise also as a result of traumatic brain injury, diabetes, or hypothyroidism. Capgras delusions have been reported even in association with migraine headaches.

Treatments can be successful, depending on the cause. Anti-psychotics can alleviate Capgras delusions, as can some drugs that treat comorbidities.

What is clear is that Capgras delusions arise as the result of some type of neural dysfunctioning.

Divide, conquer and perceive

Clues to how Capgras delusions arise come from understanding how brains generate perceptions of the world.

The way we perceive things gets divvied up to different parts of our brain. Brittany Greene/Flickr, CC BY-NC-ND

When confronted with high-value but complicated cues, brains have evolved a simple solution: divide up information and process different types of information separately.

For example, our visual system processes information about what is out there (objects) separately from information about what is happening to those objects (actions); that is, colour and shape are processed separately from motion, direction and location.

If that seems hard to believe, it’s because our everyday experience is not of those qualities being separate. A quick look around reveals an integrated experience with coloured objects moving around us.

Pathologies do arise, however, that confirm the “separateness” of the underlying mechanisms. Some individuals can see objects but not how they move in a condition called akinetopsia.

Conversely, individuals with agnosia report being able to tell where something is and what it is doing, but not what it is that they see.

Theories of mind

When it comes to people – perhaps the most high value targets we have ever to process – the same type of strategy applies.

Information about how someone looks and sounds, even how they move, is processed by brain mechanisms separate from those that help us form what is known as a theory of mind.

Capgras delusions mark a disconnect between different brain processes. Jari Schroderus/Flickr, CC BY-NC-ND

We form a theory of mind about almost everyone with whom we interact. Very often we may be left wondering what someone was thinking. For those people closest to us, though, our theories are detailed.

They help us understand who someone really is: how they feel, what they think, their beliefs, thoughts, loves, fears and so on.

In healthy brains, those two process are seamlessly integrated into coherent perceptions of others. Via mechanisms we don’t quite understand, an individuals appearance is matched with our theory of mind about the other person, and we recognise them for who they are.

In some cases, though, the integration processes break down. When it does, someone can look and sound right but will not “seem” right in terms of their personality, in terms of who they really are.

This obviously is unsettling for the sufferer, confronted with someone they recognise but who seems not to be the person they remember.

In an attempt to reconcile that dilemma the brain comes up with a simple solution: the person is not who they claim to be, but rather an impostor, a body double.

This account might explain Timothy Murray’s issues with Senator Lucas. If not – if the neuroscience is wrong – it might be time to call the Men in Black.

Join the conversation

14 Comments sorted by

  1. James Gates

    Post Doc

    Don't often lol on the conversation but Ja-makin brilliant captions!

  2. Mike Swinbourne

    logged in via Facebook

    An alternative explanation is that he is just a crazy person - not suffering from a mental illness, just crazy.

    1. Meg Thornton


      In reply to Mike Swinbourne

      So okay, I'll bite - what's the difference between having a mental illness, and being "crazy" as you put it?

    2. Mike Swinbourne

      logged in via Facebook

      In reply to Meg Thornton

      Have a read of the man's views at his website at the link provided and see for yourself.

    3. Meg Thornton


      In reply to Mike Swinbourne

      No. Could you please answer my question: what is the difference, as you see it, between having a mental illness, and being "crazy" - or in other words, how does being "crazy" differ from having a mental illness? You're the one positing the distinction, so presumably you have an answer.

  3. Ben Brooker

    inquisitive go-getter

    Hi Ricky,

    How common is Capgras Delusion?

    1. Ricky van der Zwan

      Associate Professor in Neuroscience and Psychology at Southern Cross University

      In reply to Ben Brooker

      Hey Ben

      Good question. As I mention in the article, it occurs about 1.5 times as often in females as in males. Indeed, it originally was thought of as a female delusion. Of course it is not.

      In terms of prevalence there are estimates that suggest it occurs in up to 15% of all schizophrenic presentations (Dohn & Crews 1986). Feinberg and Roane (2005) suggest that it presents in up to 4% of all psychiatric in patients.

      If you do the sums and pseudo-model that across the total population you would get a prevalence somewhere between 0.1% and 0.15% of the total population.

      However, that is likely an underestimate because there are other mediators of Capgras Syndrome. You can find a good account here: Bourget, D., & Whitehurst, L. (2004). Capgras Syndrome: A Review of the Neurophysiological Correlates and Presenting Clinical Features in Cases Involving Physical Violence. Canadian Journal of Psychiatry, 49, 719-725.


  4. Paul Rogers


    Of course, the original 1956 version of Body Snatchers was one of the great sci-fi horror films, especially for that era.

    Actually, I think the current Australian Senate has been taken over by dumb aliens, not to mention those blokes in the LNP who want to beat up schoolkids behind the dunny, and sell off the ABC and replace it with bodysnatchers of 50th anniversary fame.

    1. Jim KABLE


      In reply to Paul Rogers

      I reckon you are on (to) something - and it's not having sniffed some Cap-Gas!

      Maybe I'm in my own Capgras (Fat Cap?) delusion re those aliens running up and down the corridors in Canberra - threatening to push their fascist rorts against the people through by any means possible! Democracy - wherefore art thou - if not done to death by the aliens!

  5. Steve Matthews

    logged in via Facebook

    Really interesting, thanks for this. I had two questions. First, you're using the notion of Theory of Mind a little differently - more narrowly - to the way I understand it. I understand it as a developmentally acquired "schema" for interpreting human behaviour, my own and others. Examples of people who lack ToM are those on the autistic spectrum, who lack the ability generally to understand their world as populated by people, they just see properties or things. But I guess your usage means something…

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    1. Ricky van der Zwan

      Associate Professor in Neuroscience and Psychology at Southern Cross University

      In reply to Steve Matthews

      Thanks Steve

      My broad definition of ToM is more than just the ability to attribute mental states to oneself and to others. It includes being able to interpret what those states are likely to be (what beliefs, feels, and so on are being held).

      The issue about indifference is interesting indeed. Very often an individual will get very distressed that their loved one is not present, so sometimes there is concern. As you say, however, sometimes there is not. What one has to keep in mind is that our…

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  6. Graham Jessop


    Another take on this is that they ARE cloning people to get the results they want. This is discussed in the book 'Matthew Tell me about Heaven' by Suzy Ward, and is what the film 'Boys from Brazil' was about.
    I realise that this will be a stretch too far for most, but i believe that they have been doing this since 1939 as mentioned in the book above. Most US presidents are usually cloned to prevent them from stepping too far out of line, they know if they don't toe the line, they will be killed and a clone will replace them, unless of course the kill is televised, and that was also a warning to let them know they have to keep doing what they are told - or else. You have to wonder why anyone would be fool enough to want to be the president really. But then they are picked, way in advance of ever getting elected.

    1. Ben Brooker

      inquisitive go-getter

      In reply to Graham Jessop

      Hi Graham

      If the president is told what to do, then who is telling him/her? And why doesn't that person simply run for the presidency themselves.

      Also, are you saying a child is in it's mothers womb when it gets cloned (if they going to be roughly the same age) because its already planned that this yet born baby is going to be president one day?

      Yeah, too far of a stretch for me...