According to clinical neurologists, the left angular gyrus in particular may be involved in juggling numerical quantity, sequences, and arithmetic. When this region is damaged by stroke, the patient can recognize numbers and can still think reasonably clearly, but he has difficulty with even the simplest arithmetic. He can’t subtract 7 from 12. I have seen patients who cannot tell you which of two numbers—3 or 5—is larger.
Here we have the perfect arrangement for another type of cross-wiring. The angular gyrus is involved in color processing and numerical sequences. Could it be that, in some synesthetes, the crosstalk occurs between these two higher areas near the angular gyrus rather than lower down in the fusiform? If so, that would explain why, in them, even abstract number representations or the idea of a number prompted by days of the week or months will strongly manifest color. In other words, depending on which part of the brain the abnormal synesthesia gene is expressed, you get different types of synesthetes: “higher” synesthetes driven by numerical concept, and “lower” synesthetes driven by visual appearance alone. Given the multiple back-and-forth connections between brain areas, it is also possible that numerical ideas about sequentiality are sent back down to the fusiform gyrus to evoke colors.
In 2003 I began a collaboration with Ed Hubbard and Geoff Boynton from the Salk Institute for Biological Studies to test these ideas with brain imaging. The experiment took four years, but we were finally able to show that, in grapheme-color synesthetes, the color area V4 lights up even when you present colorless numbers. This cross-activation could never happen in you or me. In recent experiments carried out in Holland, researchers Romke Rouw and Steven Scholte found that there were substantially more axons (“wires”) linking V4 and the grapheme area in lower synesthetes compared to the general population. And even more remarkably, in higher synesthetes, they found a greater number of fibers in the general vicinity of the angular gyrus. This all is precisely what we had proposed. The fit between prediction and subsequent confirmation rarely proceeds so smoothly in science.
The observations we had made so far broadly support the cross-activation theory and provide an elegant explanation of the different perceptions of “higher” and “lower” synesthetes.4 But there are many other tantalizing questions we can ask about the condition. What if a letter synesthete were bilingual and knew two languages with different alphabets, such as Russian and English? The English P and the Cyrillic
Let me tell you about one last patient. In Chapter 2 we noted that the fusiform gyrus represents not only shapes like letters of the alphabet but faces as well. Thus, shouldn’t we expect there to be cases in which a synesthete sees different faces as possessing intrinsic colors? We recently came across a student, Robert, who reported experiencing exactly that. He usually saw the color as a halo around the face, but when he was inebriated the color would become much more intense and spread into the face itself.5 To find out if Robert was being truthful we did a simple experiment. I asked him to stare at the nose of a photograph of another college student and asked Robert what color he saw around the face. Robert said the student’s halo was red. I then briefly flashed either red or green dots on different locations in the halo. Robert’s gaze immediately darted toward a green spot but only rarely toward a red one; in fact, he claimed not to have seen the red spots at all. This provides compelling evidence that Robert really was seeing halos: On a red background, green would be conspicuous while red would be almost imperceptible.
To add to the mystery, Robert also had Asperger syndrome, a high-functioning form of autism. This made it difficult for him to understand and “read” people’s emotions. He could do so through intellectual deduction from the context, but not with the intuitive ease most of us enjoy. Yet for Robert, every emotion also evoked a specific color. For example, anger was blue and pride was red. So his parents taught him very early in life to use his colors to develop a taxonomy of emotions to compensate for his deficit. Interestingly, when we showed him an arrogant face, he said it was “purple and therefore arrogant.” (It later dawned on all three of us that purple is a blend or red and blue, evoked by pride and aggression, and the latter two, if combined, would yield arrogance. Robert hadn’t made this connection before.) Could it be that Robert’s whole subjective color spectrum was being mapped in some systematic manner onto his “spectrum” of social emotions? If so, could we potentially use him as a subject to understand how emotions—and complex blends of them—are represented in the brain? For example, are pride and arrogance differentiated solely on the basis of the surrounding social context, or are they inherently distinct subjective qualities? Is a deep-seated insecurity also an ingredient of arrogance? Are the whole spectrum of subtle emotions based on various combinations, in different ratios, of a small number of basic emotions?
Recall from Chapter 2 that color vision in primates has an intrinsically rewarding aspect that most other components of visual experience do not elicit. As we saw, the evolutionary rationale for neurally linking color with emotion was probably initially to attract us to ripe fruits and/or tender new shoots and leaves, and later to attract males to swollen female rumps. I suspect that these effects arise through interactions between the insula and higher brain regions devoted to color. If the same connections are abnormally strengthened—and perhaps slightly scrambled—in Robert, this would explain why he saw many colors as strongly tinged with arbitrary emotional associations.
BY NOW I was intrigued by another question. What’s the connection—if any—between synesthesia and creativity? The only thing they seem to have in common is that both are equally mysterious. Is there truth to the folklore that synesthesia is more common in artists, poets, and novelists, and perhaps in creative people in general? Could synesthesia explain creativity? Wassily Kandinsky and Jackson Pollock were synesthetes, and so was Vladimir Nabokov. Perhaps the higher incidence of synesthesia in artists is rooted deep in the architecture of their brains.