The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

This is not to say that his spatial sense was completely intact. Recall that he could grab an isolated coffee cup easily enough but was befuddled by a cluttered buffet table. This suggests that he was also experiencing some disruption of a process vision researchers call segmentation: knowing which fragments of a visual scene belong together to constitute a single object. Segmentation is a critical prelude to object recognition in the “what” stream. For instance, if you see the head and hindquarters of a cow protruding from opposite sides of a tree trunk, you automatically perceive the entire animal—your mind’s eye fills it in without question. We really have no idea how neurons in the early stages of visual processing accomplish this linking so effortlessly. Aspects of this process of segmentation were probably also damaged in John.

Additionally, John’s lack of color vision suggests that there was damage to his color area, V4, which not surprisingly lies in the same brain region—the fusiform gyrus—as the face recognition area. John’s main symptoms can be partially explained in terms of damage to specific aspects of visual function, but some of them cannot be. One of his most intriguing symptoms became manifest when he was asked to draw flowers from memory. Figure 2.11 shows the drawings he produced, which he confidently labeled rose, tulip, and iris. Notice that the flowers are drawn well but they don’t look like any real flowers that we know! It’s as though he had a generic concept of a flower and, lacking access to memories of real flowers, produces what might be called Martian flowers that really don’t exist.

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.