Synesthesia: When Senses Bind

Image from University of Victoria

You might find yourself smelling the perfume of roses after listening to some classical music, when there isn’t any flower near, or seeing the letters of a word in bright colors when its actually written in black ink. It wouldn’t probably cross your mind that this odd capacity had a hand in the creation of many talented individuals, from poets to artists, that learned to harness their creative gift in to the creation of their works.

What is Synesthesia?

Synesthesia is a neurological condition that leads to the automatic triggering of one or more unrelated cognitive pathways when a certain stimuli is triggered. Put more simply, when one sense is activated, for example hearing, other senses are also activated at the same time, for example taste. People can be born with this condition, but some develop it later in life.

Variations of Synesthesia

There are 5 more common types of synesthesia:

• Grapheme-Color Synesthesia: when a person percieves letters and numbers as colored.
• Chromesthesia: when sound evokes another sense.
• Spatial Sequence Synesthesia: when numerical sequences, days of the week or months of the year are perceived as having specific spatial locations(for example, seeing the days of the week arranged in a cycle).
• Taste-Color Synesthesia: when tastes are associated with specific colors.
• Touch-Emotion Synesthesia: when certain textures or sensations are associated with specific emotions (for example, feeling velvet might evoke a state of calm).

People with synesthesia express a continuity to their symptoms, meaning that, for example, the colors attributed to each letter stay the same in every scenario. While these are only the most common variations of this condition, many other less-known types exist.

History

This condition was discovered rather recently, but historical evidence leads us to believe that some important people of the past experienced this phenomenon. Focus on this subject specifically, but under different names, began in the 16th century, when people began to investigate in to the idea more profoundly. The first term for this condition came with a new wave of scientific advancements, and had its roots in color discrepancy, because all reported cases of synesthesia at the time had different senses leading to the triggering of color sensations. French physician Charles-Auguste-Édouard Cornaz (1825–1911) named it hyperchromatopsia [perception of too many colors] in his medical dissertation about eye diseases. This was because Cornaz viewed the condition as somehow opposite to the known condition of chromatodysopsie (chromatodysopsia: color blindness). In 1864, the French physician Chabalier gave the condition a new name, which emphasized that, for him, it was a disturbance of vision. He named it, therefore, pseudochromesthésie (pseudochromesthesia), because of the perception of false colors. The condition had earned several names in the decades when its understanding wasn’t complete, many basing themselves on the specific variations of synesthesia that seemed to be apparent in the people who where studied or the examiners themselves. The name we know today dates back to 1888, when French physician Henry de Fromentel introduced the term synésthesie, meaning double-sensation.

But Why Does This Happen?

While there isn’t actually a know reason why synesthesia manifests in its many forms, there are certainly many theories. Some of the most popular ones are:

• The Hyperconnectivity Theory puts forward the idea that synesthesia might be caused by increased connectivity between cortical regions, meaning that certain parts of the brain interact when they shouldn’t, due to the failure of cortical pruning(removing) of neurons.
• The Disinhibition-Unmasking hypothesis proposes the option that synesthesia appears due to a decreased level of feedback from inhibitory cortical areas, the parts of the brain that contain inhibitory neurons(a type of neuron that specializes in preventing chaotic or excessive electrical activity in the brain).
• The Learned Association theory suggests that synesthetic links are caused by learned associations early in life. This theory has been discredited because of uncovered genetic links and an increased incidence in women.
• The Awareness Theory proposes the idea that synesthesia occurs as a normal part of our perception process and the phenomenon is caused by the failure of our brain to suppress concurrent factors. This theory also hypothesizes that everyone has this condition in a sense.
• The Neonatal Synesthesia theory suggests that all humans are born with synesthesia-like tendencies, which in “normal” people are lost through age. This is a largely denied and controversal hypothesis.

Why Does Synesthesia Matter?

You might be wondering how this condition, although fascinating, has made any difference in the field of medicine. With only speculations on why this peculiar phenomenon occurs, you might even be questioning if the identification of the condition is enough to be uncovered after centuries of research. Well, while its true that there is no answer for the question of synesthesia, the effort put in to this search was definitely worth-while. Throughout the studies regarding this condition, other perception related questions where raised, leading to the discovery of new areas in this extensive field of study. Cross-Modal Perception (CMP), the cognitive process by wich sensory information from multiple sources, such as vision, audition, touch, smell, and taste, is integrated to form a coherent perceptual experience, has been theorized to play a part in the building of synesthesia. Additionally, research regarding the process also linked itself with studies regarding the condition.

Conclusion

The field of perception is a vast and predominantly unexplored area of study, because, like I mentioned before, focus has started to shift in this direction rather recently. The attention this subject receives will likely shelter important advancements. This means that, even if this condition is interesting by itself, the popularity it might gain could influence a new age of discovery in this domain.