Synesthetic Why some people can even see sounds

Synesthesia, an unusual form of perception, occurs in one out of every 25 people. In those affected, one sensory perception automatically combines with another, for example, listening to music by seeing colors.

Now, researchers from the Max Planck Institute for Psycholinguistics and the University of Cambridge report evidence of the biological causes of synesthesia. To do so, they studied families where the phenomenon occurs and describe genetic changes that may contribute to differences in perception.

Synesthetes can see, taste or perceive sounds as geometric figures. Such sensory "skipping effects" occur in a wide variety of forms and can develop in early childhood. For more than a century, synesthesia has been recognized as a family phenomenon - an indication of the important role that hereditary factors play.

"Imaging research suggests that the circuitry in the brain of adult synaesthesia is somewhat different than that of people who do not experience such particular sensory connections. But we do not know how these differences come about, "says Amanda Tilot, geneticist at the Max Planck Institute for Psycholinguistics. "We suspect that part of the answer lies in the genetic predisposition of humans."

Genetic insight into sensory experiences
In the journal Proceedings of the National Academy of Sciences, scientists from the Max Planck Institute for Psycholinguistics and the University of Cambridge are now reporting new genetic clues for the biological basis of synesthesia. For their study, the researchers examined the DNA of three families in which generations of several family members see colors in their hearing of sounds.

Using state-of-the-art methods of genome sequencing, the team was able to identify genetic variants in families with synesthesia and understand how they are passed from one generation to the next. In doing so, the researchers paid particular attention to rare DNA alterations that influence the nature of protein coding by genes and are in perfect agreement with synesthesia inheritance in each family.

Although the labeled DNA variants differ between the three families, the researchers found a common ground: an enrichment of genes involved in axonogenesis and cell migration. Axonogenesis is a key process that allows brain cells to interconnect with the right partners.

Families combine to uncover biological processes
Simon Fisher, director at the Max Planck Institute and head of the research project, says, "From earlier research by our colleagues at Cambridge, we knew that not a single gene could account for this amazing property. Even if the same type of synesthesia occurs in multiple families, there are likely to be different genetic explanations. "Fisher continues," Our hope was that the DNA data would give us clues to common biological processes, that is, to factors involved in the process Synesthesia are involved. "

Simon Baron-Cohen, director of the University of Cambridge Autism Research Center, explains, "This study reveals how genetic differences - possibly through brain alteration - can affect our sensory experiences. Synesthesia is a clear example of neurodiversity that we should respect and appreciate. "