Crossfire of Sensations

Check out my article about synesthesia: Crossfire of sensations

I wish I were a synaesthesist. “A what?” you ask. No, I am not talking about a profession or a new religious cult. Synaesthesia is a “neurological condition”, although this description hardly does it justice. Imagine a world, where every word, letter, number, emotion or music comes with its own signature colour or taste. This is what it is like for a synaesthesist. Their world is colourful and tasteful because of a crossfire of senses. Synaesthesist can have blue Mondays, yellow Tuesdays, sour evenings or green threes, amongst others.

Synaesthesia comes from the ancient Greek words syn (union, together) and aisthēsis (sensation) meaning joined sensation. And that’s what it is—two independent senses experienced together1.

There are over 60 forms of synaesthesia2. In ‘grapheme-colour’ synaesthesia, words, letters and/or numbers are in colour and are often arranged in space. In ‘lexical-gustatory’ synaesthesia, words can elicit different tastes. Music or emotion can also evoke colours, and in the mirror-touch synaesthesia, people experience tactile sensations when they see others being touched. This is also associated with a heightened emphatic ability3. In a rarer form of synaesthesia, people see auras, coloured outlines, around other people and objects1.

Surprisingly, synaesthesia is relatively unknown and unresearched. The first documented case dates back to 18124, and synaesthesia has been more systematically described by Galton (1822-1911)5 later on, but after the early 1900s, research almost ceased.

Probably around 2-4% of the population have synaesthesia6. Many synaesthesists are not even aware that they experience the world differently to others, and sometimes only discover it by chance. Synaesthesia occurs from childhood on and people usually do not tend to lose it (and if they do lose it, usually it will be before the age of seven)1. Some forms of synaesthesia can be induced, either through accident, loss of a sense or drugs. In the early 1960s, it was shown that LSD can lead to synaesthesthetic experiences1,5. But it is unclear if the mechanisms are similar.

New research into synaesthesia has only recently been picked up again; but its mechanisms and causes remain partly unknown. Structural differences in the brain and/or interactions between different brain centres are thought to explain some of the mechanisms7,8. Cross wiring and cross activation between different regions in the brain could lead to different senses being experienced at the same time. But researchers are unsure if the cross wiring between different brain areas is caused by the connectivity between neurons or by chemicals1,5.

Brain imaging studies have also revealed differences in the brain anatomy. Synaesthesists appear to have connectivity clusters and the grey matter in some parts of the brain (parietal cortex and hippocampus) is thicker than in non-synaesthesists7,8. Researchers have also found increased connectivity and activity in centres processing texture, colour and form7,8, 13. Imaging techniques revealed that depending on the type of synaesthesia, centres processing taste, visual information or emotion are more active. Others suggest that the whole brain, and not just some areas, is strongly hyper-connected9.

Cases of synaesthesia are often common among family members, suggesting that a genetic component may be passed on through genes10. Although some similarities or patterns in the sensations can be observed between people, everyone experiences different sensations or combinations, even identical twins1. These combinations usually stay for life1.

Many synaesthesists work in the artistic industry. Some famous synaesthesists include the philosopher Ludwig Wittgenstein, the musician Miles Davis, the Nobel Prize physicist Richard Feynman, the author Vladimir Nabokov, and many more5.

I have to say that I envy synaesthesists a little bit. Although their sensations can lead to an overload of experiences at times, it must be amazing to see the world in technicolours. This “additional sense” shows us how fascinating the brain is and how little we still know about all its functions. Synaesthesia opens a new window of research for neuroscientists, philosophers and linguists, not only to understand this phenomenon, but also to learn more about brain mechanisms and individual differences in perception.

1.       Cytowic, R. E., & Eagleman, D. M. (2009). Wednesday is indigo blue: Discovering the brain of synesthesia. MIT Press.

2.    Spector, F., & Maurer, D. (2009). Synesthesia: a new approach to understanding the development of perception. Developmental psychology, 45(1), 175.

3.     Banissy, M. J., & Ward, J. (2007). Mirror-touch synesthesia is linked with empathy. Nature neuroscience, 10(7), 815-816.

4.     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.

5.     Ward, J. (2013). Synesthesia. Annual Review of Psychology, 64, 49-75.

6.     Simner, J., Mulvenna, C., Sagiv, N., Tsakanikos, E., Witherby, S. A., Fraser, C. & Ward, J. (2006). Synaesthesia: The prevalence of atypical cross-modal experiences. Perception, 35(8), 1024.

7.     Rouw, R., & Scholte, H. S. (2007). Increased structural connectivity in grapheme-color synesthesia. Nature neuroscience, 10(6), 792-797.

8.     Rouw, R., Scholte, H. S., & Colizoli, O. (2011). Brain areas involved in synaesthesia: a review. Journal of Neuropsychology, 5(2), 214-242.

9.     Hänggi, J., Wotruba, D., & Jäncke, L. (2011). Globally altered structural brain network topology in grapheme-color synesthesia. The Journal of Neuroscience, 31(15), 5816-5828.

10.   Baron-Cohen, S., Burtlf, L., Smith-Laittan, F., Harrison, J., & Bolton, P. (1996). Synaesthesia: prevalence and familiality. Perception, 25, 1073-1079.