The Tell-Tale Brain

FIGURE 2.11 “Martian flowers.” When asked to draw specific flowers, John instead produced generic flowers, conjured up, without realizing it, in his imagination.

A few years after John returned home, his wife died and he moved to a sheltered home for the rest of his life. (He died about three years before this book was printed.) While he was there, he managed to take care of himself by staying in a small room where everything was organized to facilitate his recognition. Unfortunately, as his physician Glyn Humphreys pointed out to me, he would still get terribly lost going outside—even getting lost in the garden once. Yet despite these handicaps he displayed considerable fortitude and courage, keeping up his spirits until the very end.

JOHN’S SYMPTOMS ARE strange enough but, not long ago, I encountered a patient named David who had an even more bizarre symptom. His problem was not with recognizing objects or faces but with responding to them emotionally—the very last step in the chain of events that we call perception. I described him in my previous book, Phantoms in the Brain. David was a student in one of my classes before he was involved in a car crash that left him comatose for two weeks. After he woke up from the coma, he made a remarkable recovery within a few months. He could think clearly, was alert and attentive, and could understand what was said to him. He could also speak, write, and read fluently even though his speech was slightly slurred. Unlike John he had no problem recognizing objects and people. Yet he had one profound delusion. Whenever he saw his mother, he would say, “Doctor, this woman looks exactly like my mother but she isn’t—she’s an imposter pretending to be my mother.”

He had a similar delusion about his father but not about anyone else. David had what we now call the Capgras syndrome (or delusion), named after the physician who first described it. David was the first patient I had ever seen with this disorder, and I was transformed from skeptic to believer. Over the years I had learned to be wary of odd syndromes. A majority of them are real but sometimes you read about a syndrome that represents little more than a neurologist’s or psychiatrist’s vanity—an attempted shortcut to fame by having a disease named after him or being credited with its discovery.

But seeing David convinced me that the Capgras syndrome is bona fide. What could be causing such a bizarre delusion? One interpretation that can still be found in older psychiatry textbooks is a Freudian one. The explanation would run like this: Maybe David, like all men, had a strong sexual attraction to his mother when he was a baby— the so-called Oedipus complex. Fortunately, when he grew up his cortex became more dominant over his primitive emotional structures and began repressing or inhibiting these forbidden sexual impulses toward mom. But maybe the blow to David’s head damaged his cortex, thereby removing the inhibition and allowing his dormant sexual urges to emerge into consciousness. Suddenly and inexplicably, David found himself being sexually turned on by his mother. Perhaps the only way he could “rationalize” this away was to assume she wasn’t really his mother. Hence the delusion.

This explanation is ingenious but it never made much sense to me. For example, soon after I had seen David, I encountered another patient, Steve, who had the same delusion about his pet poodle! “This dog looks just like Fifi,” he would say “but it really isn’t. It just looks like Fifi.” Now how can the Freudian theory account for this? You would have to posit latent bestial tendencies lurking in the subconscious minds of all men, or something equally absurd.

The correct explanation, it turns out, is anatomical. (Ironically Freud himself famously said, “Anatomy is destiny.”) As noted previously, visual information is initially sent to the fusiform gyrus, where objects, including faces, are first discriminated. The output from the fusiform is relayed via pathway 3 to the amygdala, which performs an emotional surveillance of the object or face and generates the appropriate emotional response. What about David, though? It occurred to me that the car accident might have selectively damaged the fibers in pathway 3 that connect his fusiform gyrus, partly via the STS, to his amygdala while leaving both those structures, as well as pathway 2, completely intact. Because pathway 2 (meaning and language) is unaffected, he still knows his mother’s face by sight and remembers everything about her. And because his amygdala and the rest of his limbic system are unaffected, he can still feel laughter and loss like any normal person. But the link between perception and emotion has been severed, so his mother’s face doesn’t evoke the expected feelings of warmth. In other words, there is recognition but without the expected emotional jolt. Perhaps the only way David’s brain can cope with this dilemma is to rationalize it away by concluding that she is an imposter.⁶ This seems an extreme rationalization, but as we shall see in the final chapter the brain abhors discrepancies of any kind and an absurdly far-fetched delusion is sometimes the only way out.

The advantage of our neurological theory over the Freudian view is that it can be tested experimentally. As we saw earlier, when you look at something that’s emotionally evocative—a tiger, your lover, or indeed, your mother— your amygdala signals your hypothalamus to prepare your body for action. This fight-or-flight reaction is not all or nothing; it operates on a continuum. A mildly, moderately, or profoundly emotional experience elicits a mild, moderate, or profound autonomic reaction, respectively. And part of these continuous autonomic reactions to experience is microsweating: Your whole body, including your palms, becomes damper or dryer in proportion to any upticks or downticks in your level of emotional arousal at any given moment.

This is good news for us scientists because it means we can measure your emotional reaction to the things you see by simply monitoring the degree of your microsweating. This can be done simply by taping two passive electrodes to your skin and routing them through a device called an ohmmeter to monitor your galvanic skin response (GSR), the moment-to-moment fluctuations in the electrical resistance of your skin. (GSR is also called the skin conductance response, or SCR.) Thus when you see a foxy pinup or a gruesome medical picture, your body sweats, your skin resistance drops, and you get a big GSR. On the other hand, if you see something completely neutral, like a doorknob or an unfamiliar face, you get no GSR (although the doorknob may very well produce a GSR in a Freudian psychoanalyst).

Now you may well wonder why we should go through the elaborate process of measuring GSR to monitor emotional arousal. Why not simply ask people how something made them feel? The answer is that between the stage of emotional reaction and the verbal report, there are many complex layers of processing, so what you often get is an intellectualized or censored story. For instance, if a subject is a closet homosexual, he may in fact deny his arousal when he sees a Chippendales dancer. But his GSR can’t lie because he has no control over it. (GSR is one of the physiological signals that is used in polygraph, or so-called lie-detector tests.) It’s a foolproof test to see if emotions are genuine as opposed to verbally faked. And believe it or not, all normal people get huge GSR jolts when they are shown a picture of their mothers—they don’t even have to be Jewish!

Based on this reasoning we measured David’s GSR. When we flashed neutral pictures of things like a table and chairs, there was no GSR. Nor did his GSR change when he was shown unfamiliar faces, since there was no jolt of familiarity. So far, nothing unusual. But when we showed him his mother’s picture, there was no GSR either. This never occurs in normal people. This observation provides striking confirmation of our theory.

But if this is true, why doesn’t David call, say, his mailman an imposter, assuming he used to know his mailman prior to the accident? After all, the disconnection between vision and emotion should apply equally to the mailman —not just his mother. Shouldn’t this lead to the same symptom? The answer is that his brain doesn’t expect an emotional jolt when he sees the mailman. Your mother is your life; your mail carrier is just some person.

Another paradox was that David did not have the imposter delusion when his mother spoke to him on the phone from the adjacent room.

“Oh Mom, it’s so good to hear from you. How are you?” he would say.