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5 is blue, and A is red – short circuit in the brain or just Synesthesia?

wallpapers News 2020-07-08

“Oh, please, gentlemen, a little bluer, if you please! This key requires it!” – Franz Liszt.

Did you know that some people may see colors while thinking about numbers? Others may taste words, see sounds, or feel something on their skin when they hear a particular sound or smell a certain scent. It is a neurological condition called synesthesia, in which information stimuli activate the senses not only responsible for it but also utterly unrelated senses. In this article, we will look at what synesthesia is, its variety, and how affected people perceive the world.

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The word “synesthesia” originates from two Greeks words, “synth” (together) and “esthesia” (perception). Synesthesia is a neurological condition in which stimulation of cognitive pathways or senses causes spontaneous perceptual experience in the other cognitive pathway or senses  [1]. It was formally documented in the Chinese text during the late 1800s. The text indicates that there is a correlation between dates, colors, and flavors. Even Sir Isaac Newton attributed different colors to the music.

Synesthesia affects about 4 percent of the human population [2]. You may wonder how synesthetes can bear so many stimuli entering their brain at the same time. It must be very exhausting when all the sensory perceptions mingle and create complex forms such as colored numbers or letters. But nothing could be further from the truth. The situation resembles the way color-blind people could perceive our world. They have a narrower range of colors. The colorful world that people with normal color vision experience might be perceived as overstimulating, just like most of us think about synesthesia.


There are known cases of people who did not reveal their unusual conditions for a very long time. They had acknowledged their experience someday, but people were doubting and laughing. Since then, they have decided to keep their unusual experiences only for themselves.

Synesthetes (i.e. people affected by the phenomenon of synesthesia) do not need any medical help as is an entirely normal, although rare condition. Many people are not aware of the fact that such a phenomenon even exists. Sometimes synesthetes themselves are not conscious about their specialness and get very surprised when they find out that others do not have the same experience as they [3].

Experiencing letters or numbers with colors is the most common but not the only type of synesthesia. The most frequent is grapheme-color synesthesia, which associates letters and numbers with specific colors [4]. Another type is when both spoken and written words evoke some specific rather than basic flavor such as sweet or bitter.

For example, “suntan” may taste like salty caramel. Especially words with similar phonic patterns like “money” and “honey” or “brown” and “brownie” share the same synesthetic tastes. Some other synesthetes experience colored hearing. It is called lexical-gustatory synesthesia, in which words are associated with an exceptional taste. The sounds such as music, laughing, screaming, car honking, or dog barking trigger some colors. One voice could be golden brown, whereas the other would be light blue like frozen water.

There is also a variant in which sounds evoke tactile impressions. Different music instruments may influence the body parts in various ways. The violin’s sound can bring a feeling of stroking hair, the flute can cause goosebumps, and tingling can assist the percussion.

So, the concert orchestra can be for someone with a very comprehensive and quite emotional experience. In this way, some music can be disliked because of the unpleasant or even painful effect. This is auditory-tactile, the synesthesia type, in which sounds can produce physical sensations. There is also chromesthesia, the phenomena in which sounds make people see colors.

All these types belong to a group of projection synesthesia. An interesting type of synesthesia is the mirror-touch one. It can be defined as a kind of passionate empathy. A person affected by it feels an event as a person who is directly involved in it. Its severity may vary and may even lead to a feeling of suffocation when he saw a patient receiving CPR.

One could assume synesthesia is an endless variety. Synesthesia itself is very rare, however, even within its scope, there are many unusual combinations. The diversity of synesthesia proves how remarkable are differences within the perception of the world by each individual. Every brain actively and independently constructs reality. The reality is far more subjective than we would assume.

It is also possible to experience synesthesia temporally through psychedelic drugs like mescaline, psilocybin, and LSD. Some research also indicates a temporary synesthesia source substances like cannabis, alcohol, and even caffeine [5].


Synesthetes are born with synesthesia or develop very early in childhood. It may be genetically inherited [2]. In rare cases, as a consequence of head trauma, strokes, or brain tumors, it is also possible to become a synesthete. What is unique about synesthetes’ brains?

To begin with, the fetal brain has more neuronal areas within areas than the mature brain. During brain development, the neurons are selectively pruned, whereas others remain intact.

Why do neurons prune? Because it helps to refine neural circuits and increase network efficiency. If the synaptic pruning failed, the interconnections would persist later in adulthood. Decreased pruning results in greater activity in cross-linked pathways. Synesthetic brains show crosstalk between normally separated brain areas, which was demonstrated through neuroimaging. The activity in one part involves the activity in another. In the case mentioned before, “grapheme-color” synesthesia, the color area V4 becomes active after viewing letters or numbers [6].

We can experience the conceptual relationship between the sharp voices and sharp shapes or calming music and soothing feelings and, at the same time, have heavily pruned neuronal pathways. However, it is slightly different as it is with synesthesia. We do not have the exact deep awareness as synesthetes do have of their sensory perception. Moreover, synesthetic colors follow a similar time-course in the brain as colors evoked from the retina. Thus, a brain map of a person affected by synesthesia shows activity in areas of the brain that are inactive in a normal person.


Synesthesia links the brain and senses together in a rare manner, making the person suffering from it perceive the world wider. It is a neurological condition in which sensory stimuli elicit additional perceptual experiences. The types of synesthesia are as great as their symptoms.

The most common is grapheme-color synesthesia (connecting the letters and days of the week with colors) and sound-to-color synesthesia (connecting sheet music and sounds with colors). It can reveal itself as single or combinations of synesthesia. There is no medical or physiological treatment for synesthesia. You can just enjoy a different view of the world than the average person. You may also be more creative thinking and discovering than non-synesthetes.

This article is a joint work of Julia Ławińska (Faculty of Chemistry, University of Warsaw), Ewa Klejman (Faculty of Chemistry, University of Warsaw), Agnieszka Pregowska (Institute of Fundamental Technology Research, Polish Academy of Sciences), and (Faculty of Chemistry, University of Warsaw) as a Science Embassy project.


[1] van Leeuwen T. M., Singer W., Nikolić D. The Merit of Synesthesia for Consciousness Research, Frontiers in Psychology 2015, 6, 1850, 1-9. DOI: 10.3389/fpsyg.2015.01850

[2] Brang D., Ramachandran V. S. Survival of the synesthesia gene: why do people hear colors and taste words? PLoS biology 2011, 9(11), e1001205. DOI:10.1371/journal.pbio.1001205

[3]  Cytowic R. E., Eagleman D. M. Wednesday is indigo blue: discovering the brain of synesthesia. MIT Press, 2009.

[4]  Colizoli O., Murre J. M., Rouw R. Defining (trained) grapheme-color synesthesia. Front Hum Neurosci. 2014,8,68. DOI:10.3389/fnhum.2014.00368

[5] Luke D. P., Devin B. T. The induction of synaesthesia with chemical agents: a systematic review, Frontiers in Psychology 2013, 4, 753. DOI:10.3389/fpsyg.2013.00753

[6]  Van Leeuwen T. M., Petersson K. M., Hagoort P. Synaesthetic colour in the brain: beyond colour areas. A functional magnetic resonance imaging study of synaesthetes and matched controls, PLoS ONE 2010, 5, e12074. DOI: 10.1371/journal.pone.0012074

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