Most words, or sounds, or colors are “residents” of one sense or another. When we say the number 3, that’s all we perceive- the numeral 3. And when we listen to the Carpenters or to Beethoven, we hear music. Period.

But consider this: even without giving it a second thought we employ phrases that on the face of it make no sense. Can prose be purple? Or a dress loud? Or a mood blue? Such literary devices evoke images that enrich our language and enhance our pleasure of reading. Or consider the whoosh sign of Nike –a design intended to evoke images of speed and running, probably “tickling” the visual cortex as well as the pre-motor area. The fact that such phrases and symbols are widely used and universally understood attests to the fact that all areas of the brain are interconnected to varying degrees.


There are people who actually see numbers as colors, or taste chocolate when they hear a song; they are called synesthetes. So what’s the biological basis for this strange phenomenon?

The November 17 issue of Science Now describes research on synesthesia published in Current Biology, (Nov. 17, 2011). “Synesthesia can occur early in life due to the explosive growth of a young child’s brain, explains neuroscientist Devin Terhune of the University of Oxford in the United Kingdom. Normally, as the child grows older and brain circuits are refined, the linkages break up. But in synesthetes, for some reason, the secondary sense persists throughout life. The simplest explanation, Terhune and his colleagues believe, is that neurons in the area responsible for the extra sense are more responsive, or “excitable,” than usual, strengthening a sensory association that the person wouldn’t normally be aware of. The investigators tested their hypothesis with a technique called transcranial magnetic stimulation, which, as the name suggests, stimulates a specific part of the brain with a weak magnetic field applied to the scalp.

The researchers worked with six people who had “grapheme-color synesthesia,”—the most common form of the condition, in which letters or numbers are perceived in certain colors (the number 2 in turquoise or the letter S in magenta, for example)—and six “normal” controls. Each participant received stimulation on the scalp near an area called the primary visual cortex until they saw a flash of light known as a phosphene.

The investigators reasoned that if the synesthetes did have highly excitable neurons in the visual cortex, they would need less stimulation than the control subjects to see the phosphene. The suspicion proved correct: in fact, people without synesthesia required three times as much stimulation to reliably evoke the phosphene.”

Why is this research important?

For many reasons. By studying the extraordinary we can learn about the ordinary. Synesthesia highlights the connections between different brain areas, albeit in an exaggerated fashion. It may be very useful in understanding visual and auditory hallucinations in a variety of neurological disorders, for instance. Or just plain artists whose vision of the world trascends ours. Just witness William Blake’s, the 18th century visionary poet and painter, painting of ” the swirl of love”.

There is a theory that certain form of childhood autism is due to failure of the neuronal pruning process that is happening in the early years of life. Are synesthetes more prone to autism? Are autists more likely to be synesthetes?

I harbor a secret wish: I hope that this research will prove that that the normal connections between different brain centers can be made subject to manipulation. Wouldn’t it be nice If we could acquire such a capacity through feedback training or meditation? I have a feeling that synesthetes experience the world as infinitely richer than we “normals” do. I am envious.



Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.


  1. I loved the article about synesthesia. I am a synesthete and as a child I was always a bit reluctant to talk about it. People think you’ re a bit wacky or you’re making it up. But one day my college piano instructor told me about Scriabin’s “color” sounds. Wow! So, today if you asked me I’d tell you that the key of D flat is blue violet, Fridays are red, and July starts out yellow but fades in the last few weeks. Wacky? Maybe…but I can’t imagine not thinking that way.


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