Synaesthesia is more common in autism

Synaesthesia, a mixing of the senses where by people see colours associated to sounds they hear or link musical notes to tats, could be more prevalent in people with autism according to new research by the journal of Molecular Autism.

Scientists from Cambridge University found that whereas synaesthesia only occurred in 7.2% of typical individuals, it occurred in 18.9% of people with autism. The scientists tested and confirmed the prediction that if both autism and synaesthesia involve neural over-connectivity, then synaesthesia might be disproportionately common in autism.

Synaesthesia involves atypical connections between brain areas that are not usually wired together, so that a sensation in one channel automatically triggers a perception in another. Autism has also been suspected of triggering over-connectivity of neurons, so that the person over-focuses on small details but struggles to keep track of the big picture.

The team, led by Professor Simon Baron-Cohen at the Autism Research Centre at Cambridge University, tested 164 adults with an autism spectrum condition and 97 adults without autism. All volunteers were screened for synaesthesia.

Among the 31 people with autism who also had synaesthesia, the most common forms of the latter were ‘grapheme-colour’: 18 of them reported black and white letters being seen as coloured. Also common was ‘sound-colour’: 21 people reported a sound triggering a visual experience of colour. Another 18 reported either tastes, pains, or smells triggering a visual experience of colour.

Professor Baron-Cohen says these findings will re-focus research to examine common factors that drive brain development in these traditionally very separate conditions. “An example is the mechanism ‘apoptosis,’ the natural pruning that occurs in early development, where we are programmed to lose many of our infant neural connections. In both autism and synaesthesia apoptosis may not occur at the same rate, so that these connections are retained beyond infancy.”

Professor Simon Fisher, a member of the team, and Director of the Language and Genetics Department at Nijmegen’s Max Planck Institute, added: “Genes play a substantial role in autism and scientists have begun to pinpoint some of the individual genes involved. Synaesthesia is also thought to be strongly genetic, but the specific genes underlying this are still unknown. This new research gives us an exciting new lead, encouraging us to search for genes which are shared between these two conditions and which might play a role in how the brain forms or loses neural connections.”

Donielle Johnson, who carried out the study as part of her Master’s degree in Cambridge, said the study goes one step further in identifying synaesthesia as a sensory issue that has been overlooked in this population. “This has major implications for educators and clinicians designing autism-friendly learning environments.”

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About monicaheck
Monica Heck is a bilingual freelance writer and journalist based in Dublin, Ireland.

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