Survival of the synesthesia gene: why do people hear colors and taste words?

Abstract

Synesthesia is a perceptual experience in which stimuli presented through one modality will spontaneously evoke sensations in an unrelated modality. The condition occurs from increased communication between sensory regions and is involuntary, automatic, and stable over time. While synesthesia can occur in response to drugs, sensory deprivation, or brain damage, research has largely focused on heritable variants comprising roughly 4% of the general population. Genetic research on synesthesia suggests the phenomenon is heterogeneous and polygenetic, yet it remains unclear whether synesthesia ever provided a selective advantage or is merely a byproduct of some other useful selected trait. Progress in uncovering the genetic basis of synesthesia will help us understand why synesthesia has been conserved in the population.

Figure 1. Number-color associations for one of our synesthetes.

Figure 2. Average familial pedigrees for synesthetes composed from data in references ,,,,,, demonstrating incidence of heritable transmission from one synesthetic parent (top row) to either a female or male child (bottom row).

Squares represent males and circles females. Color intensity reflects probability of synesthesia pedigree taken from the numbers at the bottom, representing incidence of each case.