"It's kind of like figuring out that you have a belly button," says Karen Chenausky, a 30 -year-old speech researcher who lives in Somerville, Massachusetts. "At some point you just notice and start playing with it. Then you get really into it. And after a while you get bored, because you realize everyone has one. Except not everyone has this."
Karen is talking about synesthesia, an unusual and little studied condition in which a stimulus received in one sense organ causes an experience in another. Karen, for example, has one of the most common forms of synesthesia: colored hearing. For her, sound and vision mingle: the different tones of words and letters involuntarily evoke distinct and vivid colors in her mind. Russian novelist Vladimir Nabakov was similarly gifted. In his memoir Speak, Memory, he lovingly recites his own private alphabetical palette of sounds: "In a green group, there are alder-leafed f, the unripe apple of p, and pistachio t. In the brown group, there are the rich rubbery tones of soft g, paler j, and the drab shoelace of h.” Like Nabakov, Karen revels in this added perceptual dimension. "Synesthesia is an extra way of perceiving the world," she says. "The parts of the world I perceive in this way are the parts I hold most dear."
Though known for roughly the past 300 years, synesthesia — derived from the Greek words syn (together) and aesthesis (to perceive) — is still very much a mystery. Scientists don't agree on what clauses it, or even how widespread it is. According to neurologist Richard Cytowic, offer of both scientific and popular books on the subject, only one in 25,000 people automatically sees colors when hearing words, letters, or numbers.
Cytowic has tracked the source of the synesthetic experience back to the limbic system, one of the oldest parts of the brain and a site at which emotions and memories are processed. Cytowic calls synesthetes "living cognitive fossils" because he believes this kind of multi-sensory perception is as ancient as the place in which it originates. According to his theory, synesthesia may well have been our primeval way of experiencing the world — until the more rational cortex involved and filled the senses into the individual compartments. "Synesthesia is a normal brain function in every one of us," Cytowic says, "but its workings only reach consciousness in a handful. It may well be a memory of how early mammals saw, heard, smelled, tasted and touched."
Other researchers attribute synesthesia to a profusion of neural connections between the parts of the brain that control the five senses. Daphne Maurer of McMaster University in Ontario even suggests that this embarrassment of neurological riches makes all babies born synesthetes, who experience a rattle, for example, not just as an intriguing sound but as a barrage of colors, smells, tastes, and tactile sensations. Only after about the age of four months, when the infant's cortex has sufficiently matured, does the synesthesia fade. "The brains of young babies have many more neural connections than they do in later life," explains Simon Baron-Cohen, a lecturer in the department of Experimental Psychology at Cambridge University who studying the theory. "Many of the links gradually get prone back. Synesthetes may be people retain these neural connections."
"Synesthesia is not the disease," Cytowic concludes, "but a bonus. Your senses give you more the new bargained for." Though still poorly understood, the experience of Karen Chenausky and others like her suggests there's more to the world and meets the eye, ear, nose, tongue and skin. ––James Geary/London