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

“My life is spent in one long effort to escape from the commonplaces of existence. These little problems help me to do so.”

—SHERLOCK HOLMES

WHENEVER FRANCESCA CLOSES HER EYES AND TOUCHES A PARTICULAR texture, she experiences a vivid emotion: Denim, extreme sadness. Silk, peace and calm. Orange peel, shock. Wax, embarrassment. She sometimes feels subtle nuances of emotions. Grade 60 sandpaper produces guilt, and grade 120 evokes “the feeling of telling a white lie.”

Mirabelle, on the other hand, experiences colors every time she sees numbers, even though they are typed in black ink. When recalling a phone number she conjures up a spectrum of the colors corresponding to the numbers in her mind’s eye and proceeds to read off the numbers one by one, deducing them from the colors. This makes it easy to memorize phone numbers.

When Esmeralda hears a C-sharp played on the piano, she sees blue. Other notes evoke other distinct colors—so much so that different piano keys are actually color coded for her, making it easier to remember and play musical scales.

These women are not crazy, nor are they suffering from a neurological disorder. They and millions of otherwise normal people have synesthesia, a surreal blending of sensation, perception, and emotion. Synesthetes (as such people are called) experience the ordinary world in extraordinary ways, seeming to inhabit a strange no-man’s-land between reality and fantasy. They taste colors, see sounds, hear shapes, or touch emotions in myriad combinations.

When my lab colleagues and I first came across synesthesia in 1997, we didn’t know what to make of it. But in the years since, it has proven to be an unexpected key for unlocking the mysteries of what makes us distinctly human. It turns out this little quirky phenomenon not only sheds light on normal sensory processing, but it takes us on a meandering path to confront some of the most intriguing aspects of our minds—such as abstract thinking and metaphor. It may illuminate attributes of human brain architecture and genetics that might underlie important aspects of creativity and imagination.

When I embarked on this journey nearly twelve years ago, I had four goals in mind. First, to show that synesthesia is real: These people aren’t just making it up. Second, to propose a theory of exactly what is going on in their brains that sets them apart from nonsynesthetes. Third, to explore the genetics of the condition. And fourth, and most important, to explore the possibility that, far from being a mere curiosity, synesthesia may give us valuable clues to understanding some of the most mysterious aspects of the human mind—abilities such as language, creativity, and abstract thought that come to us so effortlessly that we take them for granted. Finally, as an additional bonus, synesthesia may also shed light on age-old philosophical questions of qualia—the ineffable raw qualities of experience—and consciousness.

Overall I am happy with the way our research has proceeded since then. We have come up with partial answers to all four questions. More important, we have galvanized an unprecedented interest in this phenomenon; there is now virtually a synesthesia industry, with over a dozen books published on the topic.

WE DON’T KNOW when synesthesia was first recognized as a human trait, but there are hints that Isaac Newton could have experienced it. Aware that the pitch of a sound depends on its wavelength, Newton invented a toy—a musical keyboard—that flashed up different colors on a screen for different notes. Thus every song was accompanied by a kaleidoscopic display of colors. One wonders if sound-color synesthesia inspired his invention. Could a mixing of senses in his brain have provided the original impetus for his wavelength theory of color? (Newton proved that white light is composed of a mixture of colors which can be separated by a prism, with each color corresponding to a particular wavelength of light.)