Friday, 6 January 2012

Synesthesia: not as rare as you think

Level: 3

Brang & Ramachandran. Survival of the synesthesia gene: why do people hear colors and taste words? PLoS Biol. 2011 Nov;9(11):e1001205. Epub 2011 Nov 22. 

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.

"Synesthesia may be a neurological oddity, but knowing about it and understanding the mechanisms that underpin it will help you appreciate the way the cerebral cortex functions."

Clinical significance of synesthesia:

Sensory deprivation and deafferentation (i.e., loss of sensory input through the destruction of sensory nerve fibers) can lead to synesthetic-like experiences. After early visual deprivation due to, for example, retinitis pigmentosa, touch stimuli can produce visual phosphenes, and after loss of tactile sensation from a thalamic lesion, sounds can elicit touch sensations. Arm amputees experience touch in the phantom limb merely by watching another person’s hand being touched. Hallucinogenic drugs can cause synesthesia-like experiences. 

"The article is a great read; enjoy!"