The number four is dark purple. A concert B-flat scale is light blue. Number lines can form twisted patterns, while the sight of a handshake can be felt on one’s own palm. This colourful and sensory phenomenon is a reality for thousands of people with a condition known as synesthesia. Despite the recognized existence of synesthesia since the mid-nineteenth century, the early twentieth century glorification of quantitative data excluded this qualitatively-measured condition from academic circles . As a result, not only was there a loss of scientific developments in a field rich with potential,  but there was also an entire demographic of people who faced stigma and a lack of treatment and support. However, current research efforts have begun to remedy the situation to provide information that will allow individuals with synesthesia to live better lives.
Synesthesia is a sensory condition in which the stimulation of one sense results in the processing sensation of another sense . Due to lack of research, the exact initiating factor of the condition still remains rather mysterious. However, studies have shown that synesthesia cannot be taught or learned and is instead biogenic and instinctual . There are many types of synesthesia, the most common being grapheme-colour synesthesia, in which letters and numbers are assigned specific colours . Within this subset of synesthesia, individuals can be projectors, who experience colour photisms spatially, or associators, who experience them internally in the mind’s eye .
History of Synesthesia Research
Formal research on synesthesia began in the 19th century when German physician George Sachs wrote his dissertation on his own albinism . In that paper, he touched on a completely “new” phenomenon involving colours associated with music and numbers that we now call synesthesia . Soon, more papers were published in a burst of Industrial Era productivity by scientists across a wide range of fields, including Gustav Fechner and Sir Francis Galton, the cousin of Charles Darwin [1,6]. However, this activity of synesthesia research slowed to a halt in the 1930s due to focus on external-oriented behaviorism in psychology and the difficulty of quantitatively measuring internal processes . Only twelve papers on synesthesia were published between 1940 and 1975 across the globe . As a result of this lack of information, a great stigma arose surrounding synesthesia . Symptoms of the condition were often dismissed as hallucinations or imaginations, and many synesthetes were sent home from emergency rooms without the answers they sought . To make matters more difficult, synesthetes were often condemned liars, attention-seekers, or drug-addicts in both academic and non-academic circles . Many synesthetes claimed to having been ridiculed when they told physicians and family members about their experiences and kept quiet about the way in which they perceived the world as a result . However, the cognitive revolution of the 1980s brought a new focus on synesthesia research, which has resulted in a rapidly growing field dedicated to all types of synesthesia with a particular emphasis on grapheme-colour synesthesia .
Synesthesia Advancements in the 21st Century
Modern synesthesia research often focuses on the role of neurotransmitters in synesthesia . Recent experiments show an indirect relationship between glutamate concentration and synesthetic phosphenes and increased cortical excitability in projector synesthetes . These results suggest that the increased presence of the neurotransmitter glutamate plays a role in subset determination of grapheme-colour synesthesia . Similarly, modern advances in neural network modelling allow researchers, such as computational psychiatrist at Ben-Gurion University, Oren Shriki, to map the way in which synesthesia has the potential to evolve in response to sensory deprivation or increased neuroplasticity.10 Consequently, the genesis of synesthesia is now understood to exist within a single theoretical framework instead of randomized connectivity changes.10 Concurrently, many scientists continue to expand knowledge about synesthesia by investigating the ways in which synesthesia interacts with human life.10, 13 For example, some teams focus on whether or not synesthesia “ages” alongside humanity,10 while others are dedicated to adapting synesthesia research to study consciousness .
As a result of the increasing knowledge on synesthesia, society has recently gained a greater awareness of the condition. Since the 1990s, many associations and groups have formed to support synesthetes and increase public comprehension.11 In 1995, the American Synesthesia Association was founded ; the UK Synaesthesia Association was founded soon thereafter and has held two major international conferences that have united synesthesia research and synesthetes . As well, the Synesthesia List was formed in 1993 to connect synesthetes and international synesthesia researchers across all fields .
Concurrently, the field of synesthesia research is flourishing. For example, the Palmer Lab for Visual Aesthetics at the University of California, Berkeley is currently studying the relationship between synesthesia and handedness, as a disproportionately large percentage of synesthetes are left-handed . Similarly, clinical psychologists are now using synesthesia to further understand consciousness and the way in which neural processing results in subjectivity , while social scientists are using the concept of “social synesthesia” to describe and study racial biases .
The impact of these advances extends much further than the acumen of knowledge. Much of the stigma surrounding synesthesia has begun to fade, which has allowed synesthetes to overcome feelings of isolation to form a vibrant and creative community that is full of individuals, such as Mary J. Blige, Billy Joel, and Nikolai Rimsky-Korsakov . Each of these artists, alongside the many others that fill the synesthesia community, now have a platform to discuss and legitimize their conditions. However, individuals such as Kilford, Vincent Van Gogh, and even Richard Feynman, did not have the knowledge that would have allowed them to rationalize the way in which they perceive the world to both themselves and others. In fact, it is well known that Van Gogh ended his own life in 1890, and in addition to his history of mental illness, one of the major factors that is hypothesized to contribute to his death is his supposed synesthesia . Through quotes that Van Gogh wrote in letters and journals, researchers have found his descriptions of the intense emotional pressure he was experiencing and the way in which it overcame the boundaries of his senses to consume him physically . In fact, one of the most difficult aspects of his struggles was the fact that there existed no explanation for them.
Therefore, it is imperative that the medical community continues to support synesthesia research and aid in the process of its recognition in society. After all, as demonstrated by the premature death of Van Gogh, synesthetes deserve more than the lack of information that currently exists on the subject and the travesties it can cause. Instead, they should have the opportunity to learn more about their condition so that they can get any help needed to live their best lives.
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2. Bekker, K. G., & Bekker, A. Y. (2009, December 15). Color and Emotion – a Psychophysical Analysis of Van Gogh’s Work. Retrieved October 20, 2017, from http://psyartjournal.com/article/show/bekker-color_and_emotion_a_psychophysical_analy
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4. Day, S.A. (2005). Some Demographic and Socio-cultural Aspects of Synesthesia. in L. Robertson & N. Sagiv (Eds.) Synesthesia: Perspectives from Cognitive Neuroscience. Oxford:Oxford University Press. (p. 11-33). ISBN0-19-516623-X
5. Day, S. A. (n.d.). The Synesthesia List. Retrieved September 21, 2017, from http://www.daysyn.com/Synesthesia-List.html
6. Fechner, Th. (1871) Vorschule der Aesthetik. Leipzig: Breitkopf und Hartel.
7. Jewanski, J., Day, S. A., & Ward, J. (2009). A Colorful Albino: The First Documented Case of Synaesthesia, by Georg Tobias Ludwig Sachs in 1812. Journal of the History of the Neurosciences, 18(3), 293-303. doi:10.1080/09647040802431946
8. Marks, L. E. (1975). On colored-hearing synesthesia: Cross-modal translations of sensory dimensions. Psychological Bulletin, 82(3), 303-331. doi:10.1037//0033-2909.82.3.303
9. Seaberg, M. (2015, June 03). The Future of Synesthesia Research. Retrieved October 15, 2017, from https://www.psychologytoday.com/blog/sensorium/201506/the-future-synesthesia-research
10. Shriki, O., Sadeh, Y., & Ward, J. (2016). The Emergence of Synaesthesia in a Neuronal Network Model via Changes in Perceptual Sensitivity and Plasticity. PLoS Computational Biology, 12(7), e1004959. doi:10.1371/journal.pcbi.1004959
11. Steen, C. (n.d.). American Synesthesia Association – About Us. Retrieved September 21, 2017, from http://www.synesthesia.info/aboutus.html
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13. Van Leeuwen, T. M., Singer, W., & Nikolić, D. (2015). The Merit of Synesthesia for Consciousness Research. Frontiers in Psychology, 6, 1850. doi:10.3389/fpsyg.2015.01850
14. Wannerton, J. (n.d.). About the conference. Retrieved September 21, 2017, from http://uksynaesthesia.com/2014GOLDABT.html
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