Priasha Dutta, Amity University Kolkata
Imagine visualizing alphabets or numbers in various colors when they are printed in black! Or imagine the shape “circle” bringing the taste of blueberries or the word “textbook” smelling like ground pepper! These may sound absurd but are forms of an extremely unique health condition that exists in less than 4 percent of the world’s population and more commonly in females.
What is Synesthesia?
Synesthesia(comes from the Greek words: “synth” = “together” and “ethesia” = “perception”) is a neurological condition that links two or more senses due to a single stimulus, allowing the person to experience it in more than one way. For example, when someone speaks, a synesthete can not only listen to the voice but can also associate a color, taste, smell, and physical texture with it. Synesthesia is developed from childhood or can be acquired in later years as well.
Types
There are over 60 types of synesthesia based on the various combinations of intertwining forms of the senses and cognitive pathways. For instance, the common form is Grapheme-colour synesthesia. Here, the letters and days of the week are connected with particular colors. Some others include –
- Auditory-tactile synaesthesia, where sounds induce certain sensations in the body,
- Lexical-gustatory synesthesia, where a certain taste comes to the mind on hearing any word.
- Chromesthesia or sound-color synesthesia, where a sound can make you see a certain color, sometimes even a shape and movement.
- Mirror-touch synesthesia, where an individual feels the same physical sensation that another person feels in front of them.
How does it compare to the average human brain?
Neuroimaging studies like functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) scans have documented differences in brain region activation among synesthetes compared to non-synesthetes. For example, several individuals displayed that simple achromatic graphemes can activate both grapheme regions and the color area V4 (a region of visual cortex in the brain that shows a stronger response to colors than to grayscale stimuli) in 110 ms, faster than normal individuals. They also possessed anatomical differences in the inferior temporal lobe near regions related to grapheme-color processing, such as increased coherence of white matter and increased volume of gray matter. Thus, the color-sensitive V4 region is associated with word-color synesthesia.
A conclusion was drawn that there is “cross-activation” between the color and grapheme regions and it was stated that synesthesia is because of an excessive number of neural connections between related modalities, called cross-modal associations. Scientists suggested that these connections are possible because of decreased neural pruning between the adjacent regions which are interconnected in the fetus.
Is it heritable?
Research has established that genetics have an important role to play in this as well. A total probability of 62- 66% in inheriting synesthesia by a female offspring was calculated if any one of the parents expresses this condition. In 2018, scientists used whole-exome sequencing to observe the rare genetic variants of three families, all the members of whom were sound-color synesthetes; affecting multiple relatives across generations. The study identified 37 rare genetic variants that inclined to synesthesia in each family.
Conclusion
Research suggests that synesthetes are more empathetic than others. They can have a strong inclination towards music, art, or other creative forms. Due to the capability of association, synesthetes often have an excellent memory. Their ability to process information is also enhanced in comparison to non-synesthetes.
Unfortunately, many studies carried out by neuroscientists have produced inconsistent results. This might be due to the different forms and combination patterns of synesthesia. In the future, probably with advanced neuropsychological findings and genetic data (both of rare and common variation), scientists wound find out more about the overlap between other cognitive traits and disorders and successfully explain related neurochemistry that takes place. While researchers are trying to unlock the secrets of this neurological condition, it could be safely said that synesthesia is a delight and not a delusion.
Also read: The fusion of Human cells within monkey embryos
REFERENCES–
- Brang, D., & Ramachandran, V. S. (2011). Survival of the synesthesia gene: Why do people hear colors and taste words? PLOS Biology, 9(11), e1001205. DOI: 10.1371/journal.pbio.1001205
- Hupé, J.-M., & Dojat, M. (2015). A critical review of the neuroimaging literature on synesthesia. Frontiers in Human Neuroscience, 9. DOI: https://doi.org/10.3389/fnhum.2015.00103
- Tilot, A. K., Kucera, K. S., Vino, A., Asher, J. E., Baron-Cohen, S., & Fisher, S. E. (2018). Rare variants in axonogenesis genes connect three families with sound–color synesthesia. Proceedings of the National Academy of Sciences of the United States of America, 115(12), 3168-3173. DOI: 10.1073/pnas.1715492115
- Cuskley, C., Dingemanse, M., Kirby, S., & van Leeuwen, T. M. (2019). Cross-modal associations and synesthesia: Categorical perception and structure in vowel–color mappings in a large online sample. Behavior Research Methods, 51(4), 1651–1675. DOI- https://doi.org/10.3758/s13428-019-01203-7
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