The unbearable likeness of being

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No one knew what to do about Arthur, least of all his parents. After being injured in a car crash at the age of 30, he became convinced that they were impostors, simulacra of his real mother and father. It was one of the strangest cases the brain specialist V S Ramachandran had ever encountered

I'LL NEVER FORGET the frustration and despair in the voice at the other end of the telephone. The call came early one afternoon as I stood over my desk, riffling through papers looking for a misplaced letter, and it took me a few seconds to register what this man was saying. He introduced himself as a former diplomat from Venezuela whose son was suffering from a terrible delusion. Could I help?

"What sort of delusion?" I asked.

His reply and the emotional strain in his voice caught me by surprise.

"My 30-year-old son thinks that I am not his father, that I am an impostor. He says the same thing about his mother, that we are not his real parents. We just don't know what to do or where to go for help. Your name was given to us by a psychiatrist in Boston. So far no one has been able to help us, to find a way to make Arthur better." He was almost in tears. "Dr Ramachandran, we love our son and would go to the ends of the earth to help him. Is there any way you could see him?"

"Of course I'll see him," I said. "When can you bring him in?"

Two days later, Arthur came to our laboratory. The visit would turn into a year-long study of his condition. He was a good-looking fellow, dressed in jeans, a white T-shirt and moccasins. In his mannerisms, he was shy and almost childlike, often whispering his answers to questions or looking wide-eyed at us.

The parents explained that Arthur had been in a near-fatal car accident while he was attending college in Santa Barbara, California. His head hit the windshield with such crushing force that he lay in a coma for three weeks, his survival by no means assured. When he finally awoke he seemed restored to his former self, except for this one incredible delusion about his parents. They were impostors - and nothing could convince him otherwise.

After a brief conversation to put Arthur at ease, I asked, "Arthur, who brought you to the hospital?"

"That guy in the waiting room," Arthur replied. "He's the old gentleman who's been taking care of me."

"You mean your father?"

"No, no, doctor. That guy isn't my father. He just looks like him. But I don't think he means any harm."

"Arthur, why do you think he's an impostor? What gives you that impression?"

He gave me a patient look - as if to say, how could I not see the obvious? - and said, "Yes, he looks exactly like my father but he really isn't. He's a nice guy, doctor, but he certainly isn't my father."

"But why is this man pretending to be your father?"

Arthur seemed sad and resigned as he said, "That is what is so surprising, doctor. Why should anyone want to pretend to be my father? Maybe my real father employed him to take care of me, paid him some money so that he could pay my bills." Later, in my office, Arthur's parents added another twist to the mystery. Apparently their son did not treat either of them as impostors when they spoke to him over the telephone. He only claimed they were impostors when they met face-to-face. This implied that Arthur did not have amnesia with regard to his parents and that he was not simply "crazy".

"It's so upsetting," Arthur's father said. "He recognises all sorts of people he knew in the past, including his college room-mates, his best friend from childhood and his former girlfriends. He doesn't say that any of them is an impostor. He seems to have some gripe against his mother and me."

I felt deeply sorry for Arthur's parents. We could probe their son's brain and try to shed light on his condition - and perhaps comfort them with a logical explanation for his curious behaviour - but there was scant hope of an effective treatment. This sort of neurological condition is usually permanent. But I was pleasantly surprised one Saturday morning when Arthur's father called me, excited about an idea he'd got from watching a television programme on phantom limbs in which I demonstrated that the brain can be tricked by simply using a mirror. "Dr Ramachandran," he said, "if you can trick a person into thinking that his paralysed phantom limb can move again, why can't we use a similar trick to help Arthur get rid of his delusion?"

Indeed, why not? The next day, Arthur's father entered his son's bedroom and announced cheerfully, "Arthur, guess what! That man you've been living with all these days is an impostor. He really isn't your father. You were right all along. So I have sent him away to China. I am your real father." He moved over to Arthur's side and clapped him on the shoulder. "It's good to see you, son!"

Arthur blinked hard at the news but seemed to accept it. When he came to our laboratory the next day I said, "Who's that man who brought you in today?"

"That's my real father."

"Who was taking care of you last week?"

"Oh," said Arthur, "that guy has gone back to China. He looks similar to my father, but he's gone now."

Alas, this intellectual acceptance of his parents did not last. One week later Arthur reverted to his original delusion, claiming that the impostor had returned.

Arthur was suffering from Capgras' delusion, one of the rarest and most colourful syndromes in neurology. The patient, who is often mentally quite lucid, comes to regard close acquaintances - usually his parents, children, spouse or siblings - as impostors. Although such bizarre delusions can crop up in psychotic states, more than a third of the documented cases of Capgras' syndrome have occurred in conjunction with traumatic brain lesions, like the head injury that Arthur suffered. This suggests to me that the syndrome has an organic basis. But the majority of Capgras' patients are dispatched to psychiatrists, who tend to favour a Freudian explanation of the disorder.

In this analysis, all of us as children are sexually attracted to our parents. Thus every male wants to make love to his mother and comes to regard his father as a sexual rival (the Oedipus complex), and every female has lifelong deep-seated sexual obsessions about her father (the Electra complex). Although these forbidden feelings become fully repressed by adulthood, they remain dormant. Then, along comes a blow to the head (or some other release mechanism) and the repressed sexuality toward a mother or father comes flaming to the surface; as in, "I could never feel this kind of sexual jealousy toward my real father, so this man must be an impostor." This explanation is ingenious, but then I came across a patient who had delusions similar to Arthur's - only about his pet poodle.

A better approach to studying Capgras' syndrome requires one to take a closer look at neuroanatomy, specifically at pathways concerned with visual recognition and emotions in the brain. The temporal lobes contain regions that specialise in face and object recognition - the "what pathway". We know this because when specific portions of the what pathway are damaged, patients lose the ability to recognise faces, even those of close friends and relatives. Normally, these face recognition areas (found on both sides of the brain) relay information to the limbic system, found deep in the middle of the brain, which then helps to generate emotional responses to particular faces. When I look at a face, my temporal cortex recognises the image - mother, boss, friend - and passes on the information to my amygdala (a gateway to the limbic system) to discern its emotional significance - love, anger, disappointment, and so on.

After thinking about Arthur's symptoms, it occurred to me that his strange behaviour might have resulted from a disconnection between these two areas (the one concerned with recognition and the other with emotion). Maybe Arthur's face-recognition pathway was still completely normal, and that was why he could identify everyone, including his mother and father, but the connections between this "face region" and his amygdala had been selectively damaged. If that were the case, Arthur would recognise his parents but would not experience any emotions when looking at their faces, and so would assume them impostors.

Now, this is an intriguing idea, but how does one go about testing it? When you are emotionally aroused you start sweating, not only to dissipate the heat building up in your muscles but to give your sweaty palms a better grip on a tree branch, a weapon or an enemy's throat. From the experimenter's point of view, your sweaty palms are the most important aspect of your emotional response to the face. The dampness of your hands is a sure giveaway of how you feel toward that person. Moreover, we can measure this reaction very easily by placing electrodes on your palm and recording changes in the electrical resistance of your skin. (Called the galvanic skin response, or GSR, this simple procedure forms the basis of the famous lie detector test.) For our purposes, every time you look at your mother or father, your body begins to sweat imperceptibly and your galvanic skin response shoots up as expected. My hypothesis predicted that even though Arthur saw two people he believed resemble his parents, he should not register a change in skin conductance. The disconnection in his brain would prevent his palms from sweating.

With the family's permission, we began testing Arthur. He sat in a comfortable chair, joking about the weather while we affixed two electrodes to his left index finger. Any tiny increase in sweat on his finger would change his skin resistance and show up as a blip on the screen. Next I showed him a sequence of photos of his mother, father and grandfather interleaved with pictures of strangers. I also compared his galvanic skin responses to those of six college undergraduates who were shown an equivalent sequence of photos and who served as controls for comparison. Before the experiment, subjects were told that they would be shown pictures of faces, some of which would be familiar and some unfamiliar. After the electrodes were attached, they were shown each photograph for two seconds with a 15- to 25-second delay between pictures so skin conductance could return to baseline.

In the undergraduates, I found that there was a big jolt in the GSR in response to photos of their parents - as expected - but not to photos of strangers. In Arthur, on the other hand, the skin response was uniformly low. There was no increased response to his parents, or at times there would be a tiny blip on the screen after a long delay, as if he were doing a double take. This result provided proof that my theory was correct. But how could we be sure that Arthur was even seeing the faces? Maybe his head injury had damaged the cells in the temporal lobes that would help him distinguish between faces, resulting in flat GSR whether he looks at his mother or at a stranger. This seemed unlikely, however, since he readily acknowledged that the people who took him to the hospital - his mother and father - looked like his parents. We needed to test his recognition ability more directly.

To obtain direct proof, I did the obvious thing. I showed Arthur 16 pairs of photographs of strangers, each pair consisting of either two slightly different pictures of the same person or snapshots of two different people. We asked him, "Do the photographs depict the same person or not?" Putting his nose close to each photo and gazing hard at the details, Arthur got 14 out of 16 trials correct. We were now sure that Arthur had no problem in recognising faces and telling them apart.

But could his failure to produce a strong GSR to his parents be part of a more global disturbance in his emotional abilities? How could we be certain that the head injury had not also damaged his limbic system? Maybe he simply had no emotions. This seemed improbable because throughout the months I spent with Arthur, he showed a full emotional range. He laughed, expressed frustration, fear and anger, and on rare occasions I saw him cry. Whatever the situation, his emotions were appropriate. Arthur's problem, then, was neither his ability to recognise faces nor his ability to experience emotions; what was lost was his ability to link the two.

Arthur seemed to enjoy his visits to our laboratory. His parents were pleased that there was a logical explanation for his predicament, that he wasn't just "crazy". I never revealed the details to Arthur because I wasn't sure how he'd react. Arthur's father was an intelligent man, and at one point asked me how, if the theory was correct, Arthur could still recognise him on the phone. I replied that there is a separate pathway from the auditory cortex, the hearing area of the temporal lobes, to the amygdala. One possibility was that this hearing route had not been affected by the accident - only the visual centres had been disconnected.

As we continued to test Arthur, we noticed that he had certain other quirks and eccentricities. Occasionally he would duplicate objects, including countries - at one point claiming there were two Panamas. Most remarkable of all, Arthur sometimes duplicated himself. The first time this happened, I was showing Arthur pictures of himself from a family photo album and I pointed to a snapshot of him taken two years before the accident.

"That's another Arthur," he said. "He looks just like me but it isn't me."

Arthur's inability to make emotional contact with people who mattered to him most - his parents - caused him great anguish. One day Arthur turned to his mother and said, "Mum, if the real Arthur ever returns, do you promise that you will still treat me as a friend and love me?" Philosophers have argued for centuries that if there is any one thing about our existence that is beyond question, it is the simple fact that "I" exist as a single being who endures in space and time. But even this axiomatic foundation of human existence is called into question by Arthur.

! Professor VS Ramachandran is director of the Center for Brain and Cognition at the University of California. This is an edited extract from his book 'Phantoms in the Brain', published this week by Fourth Estate, price pounds 17.99