So often in my column I am writing about ways in which the human brain can trip us up and make daily functioning in life more difficult.

In such a complex organ, small genetic differences can cause one person to experience the irrational delusions associated with psychosis, another to feel the deep pit of depression while many others may have no problems with their psychological health.

It is gratifying to be able to write about an interesting genetic condition which allows those who experience it to perceive things differently from many without it causing difficulty in life.

Synesthesia is a neurologically based condition, in which stimulation of one sense or cognitive pathway leads to an automatic and involuntary experience from a secondary one.

For example, one of the more common forms of this condition is called grapheme colour synesthesia where individuals perceive different letters and numbers as inherently tinted.

In the mind’s eye, the letter A may be red while B is green and every letter in the alphabet is linked with a specific colour that remains constant.

Instead of causing difficulties for people, this kind of synesthesia is usually reported as a pleasant or neutral experience and it can actually be helpful for memory as well as in creative pursuits. As a result, synesthesia is not considered a disorder but simply a genetic trait causing a difference in perception.

Although it is not the norm, synesthesia is not as rare as you might think. Roughly one in every 23 people experience some form of synesthesia and it affects men and women equally.

Grapheme colour synesthesia is one of the most common forms of this condition, but 60 different types have been identified.

Ordinal linguistic personification is another fairly common type of synesthesia in which days of the week or seasons are associated with specific personalities.

In number form, numbers, months or days of the week are linked with specific and precise locations in space and lexical gustatory synesthesia occurs when words in the spoken language bring on taste sensations on the tongue. In this particular synesthesia, the tastes are always reminiscent of foods eaten by the individual in early life.

Very little scientific research has been done to date on the many forms of synesthesia and it is still unknown what causes it. We do know there is some genetic basis for the condition as it runs strongly in families and seems to affect an area on chromosome two that can also be associated with conditions such as autism spectrum disorder and epilepsy. Individuals with either of these two disorders also seem to have a higher incidence of co-occurring synesthesia but the exact link between them is not understood.

The vast majority of people who experience true synesthesia, experience it from early childhood. In some cases however, it can begin after the use of psychedelic drugs, after a stroke or epileptic seizure or as a result of blindness or deafness. In these instances, it is called adventitious synesthesia and it seems to always link senses such as vision, hearing, taste or touch.

It will be interesting to learn more about this unique trait as research emerges on the subject. It is yet another mysterious and fascinating adaptation of the human brain.


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