Synesthesia Phenomenon: The Human Sixth Sense

When asked to imagine the city’s skyline, do you taste blueberries? Do the dulcet tones of a piano induce a tickling sensation on your arms? Are you convinced that Thursdays are yellow, and Fridays are blue? If yes, then you might have synesthesia.

Synesthesia is a neurological condition in which one sensory pathway (such as vision) if stimulated, sets up a simultaneous, automatic and involuntary stimulation in another independent sensory pathway (such as taste). In other words, synesthesia involves the activation of two or more unrelated senses at the same time. For instance, if a person, while hearing music, sees swirling patterns of different colours, he might have synesthesia. The word ‘synesthesia’ comes from two different Greek words: ‘syn’- which means ‘joined’ and ‘aesthesia’- which means ‘perception’. Thus, synesthesia is nothing but ‘joined perception’. Almost 1 in 2000 people have synesthesia, including the Nobel Prize winning physicist, Richard Feynman, and renowned creative minds such as Vincent Van Gogh and Vladimir Nabokov.

Synesthetic perceptions typically vary from one individual to the other. Since this condition involves interconnections between different cognitive pathways, the classification of different types of synesthesia is often a complex one. Scientists have, however, managed to come up with a more or less comprehensive classification.

This includes:

• Grapheme-Colour Synesthesia (where the individual associates letters or numbers to specific colours)
• Sound-to-Colour Synesthesia (where a particular sound triggers the visualisation of coloured, generic shapes such as squares or circles)
• Number-form Synesthesia (When a person with number-form synesthesia thinks about numbers, a number map is involuntarily visualized)
• Personification (An individual who experiences this will associate ordered sequences with various personalities. For example, a person having this kind of synesthesia may look at the letter ‘Q’ and think that ‘Q’ is a ‘rude’ letter.
• Lexical-Gustatory Synesthesia ( associating words with specific tastes)

The chances of being a ‘synesthete’ (person having synesthesia) is higher if you are a woman, left-handed or if someone in your family already has this condition. It should be noted that synesthetes are neurologically normal and generally manifest above-average intelligence, creativity and memory. This trait is generally dominant and is inherited via the X-chromosome.

Synesthesia occurs due to ‘crossed-wiring’ in the brain. Neurons and synapses, which are generally confined within a single sensory system, cross over and establish connections with neurons from a different sensory system. The limbic system, which regulates our emotional responses, is primarily responsible for this condition, though some portions of the cerebral cortex also show significant involvement. Single-sense areas of the brain receiving feedback signals from multisensory areas can also induce synesthesia.

The study of synesthesia has always interested researchers as it promises to reveal deeper concepts about the human consciousness. The biggest mystery in the study of consciousness is ‘The Binding Problem’. No one knows how we bind all of our perceptions together into one complete whole. For example, when you hold a flower, you see the different colours, you observe its shape, you smell its scent, and you feel its texture. Your brain manages to bind all of these perceptions together into an integrated whole to provide you with a single, multidimensional concept of a flower. Synesthetes might possess additional enhanced perceptions that add to their concept of a flower. Studying these perceptions may someday help us understand how we perceive our world.