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Synesthesia: Types, Causes, Symptoms, Diagnosis And Treatment

When the brain processes data in the form of several senses at once, it is a neurological condition known as synesthesia[1] . If you can taste sounds or visualize colours the moment you hear a song, then this could hint at you having this rare condition known as 'synesthesia'.

This condition is quite uncommon and its cause is yet to be fully understood. Few experts believe that its cause could be genetic. It affects more women than men[2] . It is believed that this condition commonly occurs and is more prevalent in writers, musicians and artists.

According to a leading magazine, about 20 to 25 per cent of people of these professions have synesthesia [3] . Read on to know more about this condition.

What Is Synesthesia?

People who have synesthesia (called synesthetes) may taste words, see sounds or feel a sensation on their skin when they smell certain scents[4] . The people with this condition experience a blending of two senses or perceptions. The word 'synesthesia' has been derived from the Greek word meaning 'concomitant sensations'.

Synesthetes may automatically couple sounds with colours or written letters with colours. A synesthetes might experience more than one form of synesthesia. However, researchers are yet to conclude how many types of synesthesia actually exist. The five accepted senses are sight, taste, hearing, touch and smell. A person having synesthesia is believed to experience a crossover of two senses (there could be numerous possible combinations).

Types Of Synesthesia

The most commonly reported types of synesthesia are as follows:

• Associating letters, geometric shapes or numbers with colours or patterns (colour-graphemic)[5]
• Associating various sounds with specific shapes, textures or colours (colour-auditory) [6]

The other less common types of synesthesia include the following [7] :
• Smelling a specific odour in the air when you hear certain sounds
• Seeing a specific colour when having a pain in the body
• Tasting words
• Seeing music as colours in the air
• Associating certain textures with certain emotions
• Seeing sign language as colours
• Associating a specific characteristic with time

Causes Of Synesthesia

Neuroscientists have proposed several competing theories about the cause behind this condition. The following are some of the theories related to the causes of synesthesia as laid down by renowned researchers:

Theory 1[8] : It results from an overabundance of neural connections. Under normal conditions, each sense would be assigned to a separate module in the brain. In such situations, there is limited cross-communication. However, in the brains of people with synesthesia, the boundaries do not exist or are overlapped. This leads to over communication between the modules.

Theory 2 [9] : Contrary to theory 1, theory 2 lays its analysis on synesthesia occurring when single-sense areas of the brain get feedback from multisensory areas. Under normal conditions, the information from the multisensory region would only return to the appropriate single-sense area. However, for people with this condition, the information gets jumbled.

Theory 3 [10] : It says that in spite of everyone having multiple, overlapping connections in the brain, not everyone uses them. It is said that the people who use the connections are the ones who experience synesthesia.

Some researches also indicate that this condition could be genetically inherited. In simple words, people who have synesthesia are believed to possess a high level of interconnection between the parts of the brain that are linked to a sensory stimulus.

Symptoms Of Synesthesia

There are multiple forms of synesthesia, each with its own set of symptoms. However, the following are some of the common symptoms observed when a person has this condition [11] :

• Involuntary perceptions that cross over between senses (hearing colours or tasting shapes)
• Ability to describe one's unusual perceptions to other people
• Sensory triggers that lead to the interplay between senses
A rare observation by experts is that people with this condition are usually left-handed.

Diagnosis Of Synesthesia

Although there is no medical method to diagnose synesthesia yet, people who experience the following are likely to be diagnosed with this condition:

• Having a perception that is the same each time [12]
• Having a generic perception (seeing a particular shape when you get a certain smell)
• Involuntary experience of perceptions [13]
• Projection of sensations outside the mind (seeing colours floating through the air on hearing particular sounds)
• Ability to remember the secondary synesthetic perception [14] much better than the primary one
• Having emotional reactions linked to individual perceptions

Treatment For Synesthesia

There is no treatment for synesthesia yet[15] . Few people even enjoy perceiving the world in a unique way that is beyond the ability of the general population. However, few people may also feel that this condition isolates them from others. It could get difficult for synesthetes to be able to explain their sensory experiences to others.

If you feel depressed because of this condition, please talk to a mental health professional who can help you to see the value synesthesia can add to your life. Under normal conditions, every person has a dominant side of the brain - either right or left.

A synesthetes might be happily surprised to know that both the sides of their brain harmonize nicely and can be an added advantage for the kind of work that they pursue.

View Article References
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  2. [2] Cytowic, R. E. (1989). Synesthesia and mapping of subjective sensory dimensions.Neurology,39(6), 849-850.
  3. [3] Berman, G. (1999). Synesthesia and the Arts.Leonardo,32(1), 15-22.
  4. [4] Grossenbacher, P. G., & Lovelace, C. T. (2001). Mechanisms of synesthesia: cognitive and physiological constraints.Trends in cognitive sciences,5(1), 36-41.
  5. [5] Sperling, J. M., Prvulovic, D., Linden, D. E., Singer, W., & Stirn, A. (2006). Neuronal correlates of colour-graphemic synaesthesia: AfMRI study.Cortex,42(2), 295-303.
  6. [6] Moos, A. C. (2013).Do colourless green voices speak furiously? Linkages between phonetic and visual perception in synaesthesia(Doctoral dissertation, University of Glasgow).
  7. [7] Ward, J. (2013). Synesthesia.Annual review of psychology,64, 49-75.
  8. [8] 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.
  9. [9] Harvey J. P. (2013). Sensory perception: lessons from synesthesia: using synesthesia to inform the understanding of sensory perception.The Yale journal of biology and medicine,86(2), 203–216.
  10. [10] Chiou, R., & Rich, A. N. (2014). The role of conceptual knowledge in understanding synaesthesia: Evaluating contemporary findings from a "hub-and-spokes" perspective.Frontiers in psychology,5, 105.
  11. [11] Neckar, M., & Bob, P. (2016). Synesthetic associations and psychosensory symptoms of temporal epilepsy.Neuropsychiatric disease and treatment,12, 109–112.
  12. [12] Safran, A. B., & Sanda, N. (2015). Color synesthesia. Insight into perception, emotion, and consciousness.Current opinion in neurology,28(1), 36–44.
  13. [13] Rothen, N., & Meier, B. (2013). Why vicarious experience is not an instance of synesthesia.Frontiers in human neuroscience,7, 128.
  14. [14] Lacey, S., Martinez, M., McCormick, K., & Sathian, K. (2016). Synesthesia strengthens sound-symbolic cross-modal correspondences.The European journal of neuroscience,44(9), 2716–2721.
  15. [15] Marks, L. E., & Mulvenna, C. M. (2013). Synesthesia, at and near its borders.Frontiers in psychology,4, 651.
Story first published: Thursday, May 23, 2019, 13:10 [IST]