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Synesthetists: Why some people can even see sounds


Researchers discover clues as to why synesthetes link sensory impressions

    It is estimated that synesthesia occurs in one in 25 people, an unusual form of perception: In those affected, one sensory perception automatically combines with another, for example listening to music with seeing colors.

Researchers at the Max Planck Institute for Psycholinguistics and the University of Cambridge are now reporting clues to the biological causes of synesthesia. To this end, they have examined families in which the phenomenon occurs and describe genetic changes that may contribute to the differences in perception.

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

“Examinations with imaging methods indicate that the circuits in the brains of adult people with synesthesia are interconnected somewhat differently than in people who do not experience such special sensory connections. But we don't 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 people's genetic makeup."

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 on new genetic evidence for the biological basis of synesthesia. For their study, the researchers examined the DNA of three families in which several family members see colors as they hear sounds across generations.

Using the latest genome sequencing methods, the team in families with synesthesia was able to identify genetic variants and understand how they are passed on from one generation to the next. In doing so, the researchers paid particular attention to rare DNA changes, which influence the type of protein coding by the genes and which perfectly matched the inheritance of synaesthesia in the individual families.

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

Combine families to uncover biological processes
Simon Fisher, director at the Max Planck Institute and head of the research project, says: “From previous research by our colleagues in Cambridge, we knew that not just a single gene could be responsible for this amazing property. Even if the same form of synesthesia occurs in several families, there are likely to be different genetic explanations for it. ” Fisher further explains, "Our hope was that the DNA data would give us clues about common biological processes, that is, factors that are involved in synesthesia."

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

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