Alzheimer's and Capgras Syndrome

Alzheimer's and Capgras: What can be done about the 'impostors' surrounding many people with Alzheimer's?

One of the most fascinating 'how the mind works' curiosities is the way that our minds distinguish (or fail to distinguish) some 'real person' that we know from a look-alike impostor, sometimes with a very poignantly humorous result:
On the 3rd day of a recent visit to my Alzheimer's mother and caregiving father, a casual dinner table conversation turned to the subject of their mothers, and I commented that I couldn't remember what their mothers' maiden names were. My father told me his mother's and then gently reminded my mother of her mother's maiden name. I said "Oh, OK," and went on eating, until my mother very politely turned to me and said, " And what is your mother's maiden name?" question mark w person

Where does Capgras come in to this?

Capgras delusion, or "Capgras Syndrome" is the delusion that identical-appearing impostors have replaced people or loved ones. My mother's conviction that I must be someone else's daughter was only one example of this syndrome, and was only one manifestation of it in this particular person with Capgras Syndrome.

Capgras is common in patients with Alzheimer's, and is named after the French neurologist Capgras, who first described it. Another neurologist, the fascinating lecturer V. S. Ramachandran, discusses this syndrome (and others) in this video; his story about a Capgras patient starts 2 minutes into the video:

There is also an excellent New York Times article about a person with Capgras. Here are some other examples from the research literature on this nervous-system-induced belief in the existence of a loved one's double:
Figure 1. A few among the many ways in which Capgras can manifest itself. (source)

Interestingly, and with a very humorous twist, it is in a recent French neurophysiology journal that one of the most unique cases of Capgras was recently published:
"We report the case of a patient who presented visual hallucinations and identification disorders associated with a Capgras syndrome. During the Capgras periods, there was not only a misidentification of his wife's face, but also a more global perceptive and emotional sexual identification disorder. Thus, he had sexual intercourse with his wife's 'double' without having the slightest feeling of familiarity towards his 'wife' and even changed his sexual habits. To the best of our knowledge, he is the only neurological patient who made his wife a mistress." (source)
There are at least 2 different pathways involved in this delusion, and the research on it has brought to light wonderful insights into how the normal mind identifies a loved one as a loved one by sight -- in this case, how we know that a person we see is someone we've seen before, and especially someone with whom we have an emotional connection. (source)
Fig.2 Normal face process w.o. brain
Figure 2. A schema for how we get the feeling that the person we see is a known loved one.

Notice what's changed between that figure and this one:

based on Ellis 2001
Figure 3. A schema for how someone with Capgras can recognize the features of the person in front of them as the features of someone familiar, but who no longer has the capability for a gut feeling that this is the real person.

Where is this happening in the brain?

As the next 2 figures show, both normal "face processing" and Capgras delusion start with the visual cortex at the back of the brain, the area which receives the 'raw data' of what strikes the rods and cones in your eyes. Two different pathways branch from that point, and if both paths are functioning, they meet in the area of the hypothalamus.

Normal detection (normal face processing) based on Ellis 2001
Figure 4. The simplified neuroanatomy of normal face processing. (Modified from source)

In both normal and Capgras conditions, the route through the amygdala to the hypothalamus ("identification detection") is functioning. But not so for the route for detecting emotional significance, which includes the Superior Temporal Sulcus (STS) and the Inferior Parietal Lobe (IPL). As figure 5 below shows, Capgras sufferers appear to have a faulty path for significance detection:
Figure 5. The malfunction of the path for significance detection may be the defining anatomical characteristic of the Capgras delusion. Modified from this source.
The last way-station of the significance detection route is the cingulate gyrus, which is part of the limbic lobe, the "Grand Central Station" of emotional paths in the brain. It appears also to be a necessary part of having some feeling for a person you see before you and with whom you have an emotional history.

With Capgras, seeing is not believing, but hearing is

Interestingly, for most Capgras sufferers, hearing the voice of the loved one (without seeing them) makes an end run around this delusion, because the delusion occurs in relation to what they see, not in relation to what they hear. As a result, the same person who looks to them like an impostor, sounds to them like the real person when the loved one is talking to them on the phone (while out of sight). There's more info here, here, here, and here.

Capgras in literature

A fascinating fictional example of Capgras is the novel The Echo Maker by Richard Powers. The book centers around a young man who develops Capgras from a brain injury, and offers a great deal of insight into what the world may look like to someone who has lost the ability to have a gut feeling that a loved one is familiar to them. Browse through excerpts here. There are more examples of Capgras in literature and film at the end of this Wikipedia article on Capgras.

What causes it?

Capgras is the most common type of delusion among people wrestling with psychiatric problems. Note. In fact, 1-3% of all psychiatric conditions involve this syndrome. Capgras may be at least partially caused by a malfunction in the normal chemistry of dopamine in the brain. Dopamine is essential for much of the brain's functioning, including for the ability to experience emotions as subtle as the feeling of familiarity. More info in Note 1.


Research on this Syndrome has a long way to go, since there are variations of Capgras more subtle than even this more recent refinement of the pathways shown in figures 2-5 above. In particular, there appear to be more pathways involved than those that have to do with reacting to the sight of a loved one. (example) For example, at least one blind person developed Capgras delusion toward a loved one that he clearly was not able to see (source) , and a woman developed a conviction that her daughter was an imposter during the time that her daughter was out of town and not visible to her. (source) . Neither of these cases involved the sight of a loved one stimulating the belief that the loved one was an impostor.

What the delusion can teach us about the undeluded mind

People with Capgras can appear almost psychotic when they reveal what they're perceiving (and, indeed, it is anti-psychotic drugs that are used to treat the delusion) but research on the delusion has been an equally great gift to the rest of us for understanding how we avoid delusions. The neurologist Ramanchandran mentioned earlier points out in his book Phantoms in the Brain (Chp.8 of which is about Capgras):
"...We begin with a set of symptoms that seem bizarre and incomprehensible and then end up -- at least in some cases -- with an intellectually satisfying account in terms of the neural circuitry in the patient's brain. And in doing so, we have often not only discovered something new about how the brain works but simultaneously opened the doors to a whole new direction of research." More.

There is a method to the madness

The person with Capgras is reasoning in a totally logical way, given the loss or malfunction of a specific group of neurons (more detail). As Ramachandran has written of most people with seemingly bizarre neurological problems,
"...None of theses people is 'crazy'; sending them to psychiatrists would be a waste of time. Rather, each of them suffers from damage to a specific part of the brain that leads to bizarre but highly characteristic changes in behavior. They... see things that no one else does, deny the obvious and make wild, extraordinary claims about other people and the world we all live in. Yet for the most part they are lucid, rational and no more insane that you or I."
Thus, there is a logic even to this seemingly off-the-wall question from a capgras patient to his caregiver: "Are you really my nurse, or are you a snake sheriff?"

A few days after I returned home from the visit to my parents, I got an email from a sister who lives in town with them: "Mom ... still has hallucinations (two men who look like Dad take care of her now) and this morning she called to tell me she's getting married" to one of the 2 men. Mother was unclear as to which of the 2 copies of Dad would be the lucky groom, but it was clear that she no longer sees Warren (our father) as the person to whom she is already (and has long been) married.

When I called my parents a few days later, my mother was still focussed on it ("Did I tell you I'm getting married?"), so I congratulated both of them happily. And my father, long experienced at rolling with the punches of Mom's Alzheimer's, said casually "Oh, yeah, I'm marrying her and the other Warren is performing the ceremony..."
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