Author: Karen Liu
Editor: Kira Tian and Katelyn Ma
Artist: Denise Suarez
Imagine seeing colorful swirls or tasting different flavors every time you hear a noise. Sounds impossible, right? Well, not for people with synesthesia. Synesthesia is a neurological disorder that causes your senses to mix together. Synesthesia occurs when one of the five senses, upon stimulation, triggers experiences in another unrelated sense. Its name is derived from the Greek roots “syn” and “aesthesis”, meaning “to perceive together”.
Synesthesia was first discovered in the 19th century when scientists noticed that certain people saw every single number or letter tinged with a particular color, even though they were all written in black ink. This condition, known as grapheme-color synesthesia, is the most common variant of synesthesia; over 60% of synesthetes experience it. Research has also shown that around 2-4% of the general population experiences synesthesia.
There are over 80 types of synesthesia, but not all are studied as extensively as others. Some synesthetes hear, smell, taste, or feel pain in color. Others have something that researchers call “conceptual synesthesia”, where they see abstract concepts such as units of time or mathematical operations projected internally or in the space around them. Synesthesia can even come in an extreme form when one experiences physical pain when they see others hurting. However, the most common forms include associating letters, numbers, or sounds with colors, sounds and shapes with tastes, and certain days or months with characters.
Synesthesia is still not well understood by scientists and the exact cause is unclear. Studies have confirmed that synesthesia is genetic, automatic, unlearned, and distinct from hallucination. It tends to run in families and is a lot more common in women than men. Recently, modern brain imaging and molecular genetic technology reveal that the condition is caused by an overabundance of connections between sensory regions of the brain, but there is still uncertainty about the neurological aspect of it. Baron Cohen, PhD, who studies synesthesia at the University of Cambridge, proposes that different sensory functions are assigned to separate modules in the brain with limited communication between them. Synesthetes have a different brain architecture equipped with more connections between neurons, causing this usual modularity to break down. Daphne Maurer, PhD, a psychologist at McMaster University, further speculates that all humans may be born with the neurological connections that allow synesthesia, but slowly lose it as we age. By four months, overlapping neural connections are pruned out and the vision center is separated from the hearing. The failure in this process is believed to give rise to synesthesia.
In terms of genetics, a 2018 study published by the journal Proceedings of the National Academy of Sciences conducted by scientists from the Max Planck Institute for Psycholinguistics and the University of Cambridge took advantage of genome sequencing to identify genetic variants in the genome of synesthetes and track how it’s passed down. They took the DNA of three families in which multiple members across several generations experienced seeing color when they hear sounds. The results showed that although the DNA variants differed between the three families, there was one common factor: an enrichment for genes involved in cell migration and axonogenesis, a key process that allows the brain to send signals to its target cells. The results show that there’s not one specific gene that accounts for synesthesia, even between families that experience the same variation of this condition. Overall, the research demonstrates how genetic variation can alter neurological pathways to the brain, modifying sensory experiences.
With all this being said, what is it actually like to have synesthesia? The experiences of synesthetes are unique and may vary from person to person. For instance, one synesthete may claim that number 4 is red, but another may argue that it’s yellow. Synesthesia is not able to be controlled and is involuntary. For instance, let’s say you were looking at a picture of flowers. Your brain automatically thinks “flowers” even though the word isn’t written over the picture. Your brain automatically makes that connection, which is the same exact process that happens when synesthetes associate multiple senses. It’s not exactly the same thing as a hallucination, though, because it’s not interfering with your ability to see. You can picture an object sitting in front of you, but it doesn’t prevent you from seeing through and past that. Most of the time, these visuals are only perceived in your mind. Only a few synesthetes can see colors outside their body. Synesthesia isn’t related to memory either. Non-synesthetes can teach themselves to associate a color with a number, but their brain wouldn’t respond in the same way as a synesthete’s brain would.
A key question here is how synesthesia has survived for this long, considering the fact that there is no benefit correlated with this condition. Now, scientists are finding answers from the synesthetes themselves. Artists, poets, novelists, and musicians are seven times more likely to have synesthesia compared to the general population. Famous painters such as Vincent Van Gogh and Wassily Kandinsky are known to have chromesthesia, in which sound evokes color, shape, and movement. Even artists today like Billie Eilish, Pharell Williams, and Charlie XCX have synesthesia. The reason behind this is best explained by the fact that the gene mutants in synesthesia not only links sensations, but also unrelated ideas, which sparks greater creativity.
Though some synesthetes are embarrassed or uncomfortable at times, most synesthetes consider this ability as a gift and wouldn’t want to lose it. Altogether, synesthesia is not a mental illness and is instead a rare neurological phenomenon marked by a fresh way to experience the world through a mixture of senses unique to the individual.
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