Synesthesia and Autism

In reading the book “Born on a Blue Day”, the author Daniel Tammet recounts how his perception of numbers as colors allowed him to remember pi to the 22,514th digit. Tammet and others believe that this ability to weave together different aspects of perception may account for unique gifts and talents. People with this ability see the world through glasses different to those used by the rest of the general population.

When seeing an object some neuronal ensembles (i.e., groups of cells within the brain) encode its shape while other ensembles encode other aspects of perception (e.g., color, movement). All of this information is placed together in a single perception or experience. As an example, olfaction and taste are usually both required to work together in order to provide a satisfactory dinning experience. Having lost your sense of smell causes some people to change their eating habits because ultimately food becomes less enjoyable. In essence being able to put together different aspects of perception allows for their synergism and the expression of emergent aspects of cognition and emotion.

For some people the putting together of different aspects of perception cross borders. Flavors come with sounds and numbers come with colors. This phenomenon is called synesthesia. Although the phenomenon of synestheia is highly appealing and has been known for a long time, the subject has not attracted as much research as it deserves. One of the first papers on the subject dates back to the time of Sir Francis Galton (Darwin’s cousin) who wrote an article entitled “Visualized Numerals” in 1880.

People can have multiple types of synesthesias. A person can acquire synesthesia when they loose one of their senses (e.g., car accident, stroke). This fact suggests that synesthesia can be acquired by the reawakening or reinforcing latent neuroanatomical pathways. In this regard people who have gone blind may see flashes of light while experiencing music. Researchers who have examined these individuals have shown that their occipital cortex (usually the brain region used for seeing) may be activated when listening to music. Another possible explanation is that the sensory modalities themselves are normally associated at a basic level during development. As an infant uses magnetized letters to learn how to read, the activity may provide associations between the color of the letters and the letters themselves.Some people may be better at finding these connections and retaining the same.

Synesthesia may be 3 times as common in autism spectrum disorders as in neurotypicals. The high prevalence of synesthesia in autism may be a reflection of changes in connectivity evidenced in the white matter of the brain. However, contrary to what is seen in autism, synesthesia is more common in women (8X) than men. It is also more common among left handed individuals. Physical and neurological examination of synesthetes reveal no additional findings. Many famous artists have had synesthesia or have used this device in their artistic expression.

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