Synesthesia

This is the neuroscience part of the blog

I’m reading The Man Who Tasted Shapes by Richard Cytowic, M.D.[1] This book is about the phenomenon of synesthesia, where a sensory stimulus triggers sensations by several senses, such as a visual stimulus producing a sound. Dr. Cytowic describes an encounter with one of his friends who, upon tasting the dinner he was preparing stated, “Oh dear, there aren’t enough points on the chicken.”  Being the observant scientist that he was, Dr. Cytowic probed further to discover that this man felt shapes when he tasted food.  Having known about synesthesia prior to this encounter, Dr. Cytowic assured his friend that his condition had been observed before. This was a great relief to his friend, who felt he could not share his observation with others without being accused of being ‘crazy’. Dr. Cytowic describes his quest for discovering more about synesthesia, unearthing reports about it from as early as 1790. The historical accounts are fascinating as are the reports about well-known visual artists and musicians who had this condition.

What was the most fascinating to me was the neuroscience, where involvement of the ‘limbic brain’ in synesthesia was hypothesized. Unlike the cortex, the outer layer of the brain that is also called the ‘gray matter’, the parts of the brain comprising the ‘limbic system’ are arrayed at its edge. Dr. Cytowic devised experiments to show that the ‘gray matter’ was not involved in synesthesia.

The word ‘limbus’ means border or margin of a structure. Paul Broca, in 1878 described anatomy of the limbic lobe of the brain as including the cingulate gyrus, the hippocampal lobe and the olfactory lobe, all structures along the midline of the brain.[2]  James Papez wrote remarkable a paper published in 1937 called A Proposed Mechanism of Emotion.[3]  He proposed that there was a pathway in the brain for emotions, organized in the same way as those that allow us to sense our environment (such as vision and touch).  ‘Papez Circuit’ included the structures of the limbic lobe identified by Broca, in large part. The fact that there are connections of limbic structures with virtually all other parts of the brain[4] gives one the idea that the limbic brain can have an enormous influence on the brain’s output, that is, the way we act or feel. With all the connections available, it makes perfect sense that some people make connections that allow them the pleasure of hearing colors or tasting shapes. Dr. Cytowic states that it is the limbic system that moderates the importance of things; ‘an emotional calculation rather than a logical one that animates us’.

I still love Mr. Spock from Star Trek. However it is emotions that help us live long and prosper.


[1] Cytowic, R.W. The Man Who Tasted Shapes, MIT Press (1999)

[2] Lautin, A. The Limbic Brain, Kluwer Academic/Plenum Publishers (2001)

[3] Papez, J.W. A proposed mechanism of emotion, Arch. Neurol. Psychiatry, 38, 725-734 (1937)

[4] Swanson, L.W. Chapter Entitled, Limbic System, in Encyclopedia of Neuroscience  G. Adelman, ed. Birkhauser (1987)

2 thoughts on “Synesthesia

  1. It is balance, too, through which we live long and prosper. Sensation and emotion are distinguishable. We sometimes lose, and researchers confuse in definition, if not careful. Among important structures are the corpus collusum. Of all the ‘connectors’, this organ of the brain appears the most connected. ‘Feeling’, we ‘think’ with the sensations of our entire body.

    These neural connections are more immediately instantaneous and direct than the reptilian brain. Each of us senses our sensations individually. Cognition could be defined as the individual organization of our sensations. In the Healing Garden, we assume it is our social education helps us bundle these sensations into articulated emotions. — The Healing Garden gardener

    Cf. Histologie du Systeme Nerveux de l’Homme et Des Vertebres, S. Ramon Y Cajal. 1972

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    • A very important discovery in brain function was made by James Papez in 1937 when he found a ’emotional circuit’ in the brain. Similar to other brain-mediated sensory functions, the emotional circuit (also known as the Limbic Brain) had a thalamic relay. So yes, sensory inputs are fed into the brain in an organized fashion, the hypothalamus, like the olfactory system, sniffs out hormonal levels in the blood and feeds it into the limbic system, which mediates emotion and memory. However, I agree that socialization and social education is an important factor in emotional development.
      Thanks,
      Jack

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