"Overview of Genetics"

Eighteen-year-old Sean Maxwell has always perceived the world in an unusual way. To most people, color is a characteristic of an object-a cherry is red; a hippo, gray. To Sean, colors are much more. When he plays a note on his guitar, or hears it from another instrument, a distinctively colored shape pops into his mind. His brain, while perceiving the note as an E flat or a C sharp, creates an overwhelming feeling of iridescent orange-yellow diamonds, or a single, shimmering sky blue crescent. Soaring crescendos of sound become detailed landscapes, peppered with alternating black and white imagery that parallels the staccato notes. These images flash by his consciousness in such rapid succession that he is barely aware of them, yet they seem to burst through his fingers in the patterns of notes that he plays. Sean has experienced these peculiar specific sound-color-shape associations for as long as he can remember, but never thought much about it. Didn't everyone link music to imagery? Then he reads a science blog about a condition called synesthesia that mixes up the senses. Synesthesia was once thought to be extremely rare, affecting only about 1 in 2000 people. But as more and more "synesthetes" are finding one another through shared strange sensory stories on the Internet, it is becoming clear that possibly as many as 1 in 23 people has some form of the condition. Rather than experiencing it as a disability, synesthetes report that they can actually harness their sensory associations to enhance learning. It isn't surprising that the condition is about eight times more common among artists and novelists than among people in other fields. Sean is so excited by what he's read about synesthesia that he decides to talk about it at dinner when he's home from college one weekend. It's easy to slip it into a discussion, for the Maxwells are a very musical family. Sean's dad, Peter, sings in various cover bands, and Sean is in a band too, playing lead guitar.
"For me, notes have colors. But for most synesthetes, letters or numbers have colors. Or time is colored, maybe days of the week, or months. It gets even stranger. Some people taste triangles or smell colors," he says between bites.
Sean looks around at his oddly quiet family, who usually interrupt one another constantly. His mom, Ellie, is focusing on her salad, while his 16-year-old sister Keri twirls her finger against her head, as if Sean's lost his mind. But his dad and 12-year-old sister Anna are each holding their forks still and are simply staring at him, their mouths agape, eyes wide.
"What?" says Sean. "Do you think I'm weird? What is it?"
Peter and Anna are silent a bit longer, as if deciding what to say. Then Peter pushes his long red hair back and says, "Not exactly. I understand."
"You do?" says Sean, astonished.
12"Yes," Peter says, looking embarrassed. "Notes have always been colored for me. I see the colors vividly when I play. The notes have textures, too. Some notes are shiny, while others seem to have a matte finish. But I never told anyone. Actually, I never even thought about it until now, and I never heard of syn whatever you called it. Sounds like an acid trip."
"Synesthesia. And you're right, LSD does cause it, temporarily. But an acid trip will give you different colors for the same notes at different times. Synesthesia doesn't work that way. It's consistent. Also, most people who have synesthesia remember it from early childhood. Speaking of which, are you sure you didn't mention it to me, like when I was six and you taught me to play guitar? Maybe I just subconsciously copy you."
"No, I'm quite sure I never said anything. I just thought it was some quirk, maybe even normal. A B flat minor chord is shiny green, and G major seventh speckled indigo. Notes have shapes, too." Peter looks sheepish.
"Yes! Shapes! But you've got the colors all wrong," exclaims Sean, jumping up. "B flat minor is pink, and G major seventh lavender, sometimes with stripes."
Father and son continue to compare their synesthetic perceptions, growing more and more excited, until Anna speaks up.
"I've got it too."
"What?" ask Sean and Peter.
"But not like you two," Anna continues. "Maybe that's because I'm not musical, like you are. Instead, I see letters and words as colors. I thought it was just a little trick I use to study-it's easier to memorize colored words."

Now father and son gaze at Anna in amazement, as Ellie and Keri, the only ones still eating, look puzzled. "Well, I'm afraid my sensory life is boring-everything's what it's supposed to be to me! No colors to sounds, or anything like that. Must've come from your side, Peter," concludes Ellie. "But maybe I'm missing out," she adds. "You are. Dad and I aren't the only musical synesthetes," says Sean. "Tori Amos says that although specific groups of chords have colors, no two songs are alike. John Mayer has synesthesia too, and so did Franz Liszt, Duke Ellington, and Leonard Bernstein." Peter's mind is racing. He can't wait to tell his bandmates. Synesthesia comes from the Greek: syn for "together" and aesthesis for "to perceive." The sensual associations of synesthesia are involuntary and highly specific, and they persist over a lifetime. The condition has been recognized since at least 1883, when Sir Francis Galton, a cousin of Charles Darwin who was an early supporter of eugenics, described it in an article in Nature magazine as a "mingling of the senses" that "runs in families." Studies since then have shown that a blood relative of a person with synesthesia has a 4 in 10 chance of also having the condition. How does synesthesia arise? Are mixed up senses merely a matter of taking a metaphor too far, such as a sharp cheese or bittersweet symphony? Or do persistent mixed senses reflect childhood associations, formed at a critical period in brain 23development, such as remembering the colors of letters in a book from which a child learned to read, or recalling colored refrigerator magnets in the shapes of letters. Brain imaging studies and genetics have shed light on the biological basis of synesthesia, but it is still not well understood. For example, functional magnetic resonance imaging of the brain focuses on neighboring parts of the cerebral cortex that process numbers and color. When a nonsynesthete looks at a string of numbers or letters, only one brain center lights up; when a synesthete who associates numbers or letters to colors watches, both brain parts light up. Perhaps synesthesia arises in the fetus, when extra connections (synapses) between brain neurons form and would normally be trimmed back. In synesthetes these extra neural links may remain, similar to a bush that hasn't been sufficiently pruned. The discovery of colorblind synesthetes localizes the phenomenon clearly to the brain. The eyes of these men lack the receptors for color vision, but their brains fill in colors for visual images. The different manifestations of synesthesia may reflect the fact that different neurons are pruned in different individuals. The degree to which genetics causes synesthesia isn't known. One study found that four specific parts of the human genome vary in a certain way among synesthetes much more frequently than among nonsynesthetes. The results of this genome-wide association study led researchers to several genes already known to be associated with autism, seizures, dyslexia, and long-term memory and learning. In fact, many people with autism who are "savants," possessing incredible talents, are synesthetes too. Researchers now think that inheriting combinations of variants in several genes, plus environmental influences, causes synesthesia. For example, if Peter and Sean weren't musically gifted, they might not have noticed their synesthesia. Because synesthesia can differ within a family, such as Anna's coloring of language instead of music, the genetic cause is likely a fundamental brain change that is expressed differently depending upon other gene variants and experiences.

QUESTIONS FOR RESEARCH AND DISCUSSION FOR "Overview of Genetics"

1. What criteria would you use to determine whether synesthesia is a disorder or a variation of normal sensation and perception?

2. Why do you think that synesthesia is more common today than it was 20 years ago?

3. Why might it be possible for infants to have synesthesia, but the ability is gradually lost?

4. Would you want to take a genetic test for synesthesia? Cite a reason for your answer.

5. Do you think that synesthesia should be regarded as a learning disability, an advantage, or neither?