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When Senses Collide: Exploring the Mysteries of Synesthesia

Brang, David, and V. S. Ramachandran. “Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words?” PLoS Biology, vol. 9, no. 11, 22 Nov. 2011, e1001205, PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC3222625/

By Tara Gandhi

This article will explore synesthesia, including its expression, possible causes, and the reasons for its continued research interest. 


Introduction:

Synesthesia is a rare neurological condition in which stimulation of one sense automatically triggers another, blending one’s perception in unusual ways. For example, someone with synesthesia might see the number 5 not only as red but also as grainy, which is a sensation that is real to them, not imagination or exaggeration. It is involuntary, meaning that synesthetes (people with synesthesia) cannot induce synesthetic experiences at will. It is a rare condition that affects approximately 2-4% of the population. People who have it often see colours attached to letters or numbers, hear sounds that seem to create shapes or colours, feel touches when they watch someone else being touched, or even sense textures, tastes, or emotions linked to words and music.


Causes:

Synesthesia has many causes and can emerge after brain injuries, sensory deprivation (losing one sense), the usage of drugs, and can even be passed down from parents. 


One of the most probable causes is the extra communication between brain regions. Sensory areas in the brain, such as the visual cortex (for seeing), the auditory cortex (for hearing), and the somatosensory cortex (for touch), can begin to communicate more than usual, causing one sense to trigger another automatically. A likely reason for this is reduced neural pruning during development, as the brain typically prunes excess connections and neural pathways as we grow; however, in people with synesthesia, some of these extra links may not be removed, so senses remain more interconnected than usual. 


Synesthesia is also theorised to be polygenic (a trait controlled by multiple genes) and heterogeneous (the same trait arising from different genetic variants), suggesting that people can inherit it from their parents and pass it down from generation to generation. This is supported by data that reveals that 40% of synesthetes have relatives with the condition. 


Some researchers suggest that synesthesia may simply be a side-effect of other useful traits, with the genes that cause it remaining in the population because they aren’t harmful enough to be eliminated by evolution. Moreover, it is also possible that synesthesia represents the end of normal cross-modal perception (the brain’s ability to combine or link information from different senses), since everyone’s brain shows some interaction between senses. 


How it works:

Synesthesia happens because some brain regions are unusually connected, so one sense can automatically trigger another. Experiencing synesthesia involves both bottom-up processing, in which sensory input directly gives rise to perception, and top-down influences, in which attention or context can alter what is perceived. For example, focusing on small or large details within a visual pattern can alter the perceived colours. Research shows that synesthetic colours appear in the brain very early, around 110 milliseconds after interacting with the stimulus, almost at the same time as normal sensory responses, indicating the immediacy and intuitiveness of synesthesia. Additionally, structural differences in synesthetes, such as increased white matter (areas of the brain where signals are relayed) and grey matter (areas of the brain where information is processed) in relevant sensory regions, suggest enhanced connectivity between the senses underlie these unique experiences.


Cognitive Benefits:

 Those with synesthesia do not only experience significant creativity and innovation due to their unique perception of the world and ability to represent their experiences artistically, but also memory advantages as well. Some synesthetes have exceptional memory, as they can use their synesthetic experiences of colours and textures as memory anchors (associations that help the brain remember things easier) for remembering numbers and words. Moreover, synesthetes often show enhanced sensory abilities like how grapheme-color synesthetes see and distinguish colors more accurately, while mirror-touch synesthetes have heightened tactile sensitivity, and motion-sound synesthetes process visual rhythms as precisely as others process sounds.


Scientific Curiosity:

Scientists are fascinated by synesthesia because it lies at the boundary between sensation and meaning, allowing abstract experiences, such as emotions, to be linked to sensory qualities providing a rare window into how the human brain constructs perception, language, concepts, and creativity. This can help develop multisensory learning tools to optimise different learning styles and insights into cross-modal processing can inform AI algorithms that mimic human perception and multisensory integration. Research into synesthesia can also tell the design of therapies for sensory disorders, stroke rehabilitation, and brain injury recovery, making it a powerful tool across the fields of education, technology, and healthcare.


Conclusion:

Overall, synesthesia is a rare and intriguing condition that automatically and consistently blends senses, creating a diverse range of cross-sensory experiences. It is likely caused by increased neural connectivity and altered pruning, as well as genetic factors. It has endured through evolution possibly due to its benefits such as memory and sensory precision. Synesthesia highlights the brain’s extraordinary capacity to connect the senses, offering a window into how perception, memory, and creativity intertwine.


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