Synesthesia

Do you ever see colours while hearing a piece of music? Or taste the flavor of food when you see certain shapes? How about feeling a sense of touch, when you’re actually looking at someone else being touched?

If these sound relatable, it’s highly possible that you have synesthesia (or synaesthesia, depends on how you spell it)! This phenomenon used to fascinate me to the point of buying a book, which I’ll be referring to throughout this post, so keep an eye on that…

What’s this “Joined Sensation”?

The term, derived from Greek words σύν syn, “together”, and αἴσθησις aisthēsis, “sensation“, refers to the interplay of multiple sensations–the stimulation of one sensory/cognitive pathway triggers another. On the other hand, anesthesia means–that’s right, no sensation! But, this connection is a consistent and involuntary one, which means that a synesthete–person who has synesthesia–makes the exact relationship between two sensations without thinking. For example, one may always make the connection between number 2 and color green. Estimation has it that about 3 to 5 % of the world population are synesthetes; believe it or not, it is more common than originally predicted.

What Caused It?

Apparently…one tends to genetically inherit synesthesia; however, interaction to various concepts at an early age also plays a role. 

The basic idea is this: synesthesia is the result of increased cross talk between various brain areas. In grapheme-color synesthesia, one’s V4 color area in the visual cortex will be activated greater than the non-synesthetic controls.

But this is not the only location though! Never overlook the brain parts that control memory, affect, and attention. Even the simplest circuit is more involved, which includes parts such as auditory cortex, parietal neurons, and V5 for movement. Studies have verified that synesthetic experience triggers the same brain parts as real-world experience. Moreover, some propose structural brain differences, for example, increased grey matter and greater neural connectivity.

Different Types of Synesthesia

Due to the variety of ways we can transcribe genes, there are about 60 to 80 different types of synesthesia so far. And what amazing combinations they include! We’ll be taking a glimpse at some here.

• Grapheme-Color Synesthesia

One experiences color synesthesia when seeing letters and/or numbers. Believe it or not, these associations vary from one to another. Interestingly, when letters form words, the colors may drastically change, according to context. Usually, the color will be more affected by spelling than pronunciation (eg. EROS vs ARROWS). 

• Mirror-Touch Synesthesia

This is a rarer condition–when one sees someone is being touched, he/she will have the same sensation. By merely viewing the action, one can activate the mirror neurons! While one may express stronger empathy than others, this type can be disruptive to one’s life. So doctors treat it as a sensory processing disorder.

One of the most common synesthesias, this refers to one being able to see color and shape when hearing sounds, especially music. Generally, synesthetes respond to acoustic/musical properties such as pitch, timbre, key, chords, and volume. No wonder people also call it “colored hearing”! 

• Lexical-Gustatory Synesthesia

Can spoken and written words evoke specific, synesthetic tastes? Of course! These synesthetes literally experience the sensation of “on the tip of the tongue”. Taste can be elicited by its corresponding food name (eg. “onion” tastes like onion), as well as words with similar phonemes (eg. ‘Kelly” tastes like jelly…hmm).

• Number Form/Spatial-Sequence Synesthesia

One will be able to visualize a mental map that consists of numbers, which can twist and loop around in all kinds of ways. This does not indicate any particular level of mathematical proficiency, however.

Notable Figures

Through the course of history, there have been quite some notable synesthetes, including…

• French composer Olivier Messiaen (1908-‘92), who was long fascinated by color and colored light since childhood. To him, music and color triggers each other mutually. He even invented a compositional method that evokes music of coloured landscapes.

• Russian painter Wassily Kandinsky (1866-1944), who combined color, hearing, touch, and smell—four senses together synesthetically! Seeking a universal translation among senses (even though we know it’s impossible), he wrote theoretical works on such ideas, including this 1911 book. 

• Russian-American writer Vladimir Nabokov (1899-1977), who is known for synesthetic references hidden within words, and whose writings greatly appeal to human senses. Perhaps he is a perfect example of the condition’s inheritance: his mother, his wife, AND his son Dimitri all had synesthesia!

Significance

Synesthesia has fascinated scientists for over 2 centuries. As more and more scientific publications shed light in this field, I cannot help but wonder the sheer vastness of unknown knowledge there exists. Questions arise all the time…Synesthesia is a neurological phenomenon; still, we can explore much more in its mechanism though!