The objective criteria that crystallises synesthesia as having a neurological basis have emerged over the last 20 years with new machines and incumbent testing procedures. Cortical metabolism, it has been shown, drops dramatically in the left hemisphere of the brain during synesthesia (18% in one individual). This seems counter-intuitive, because cerebral blood flows are actually decreased at a time when you might expect them to increase i.e. because the brain appears to be being more stimulated rather than less. This is is contrast to such activities as inhaling oxygen, or doing a crossword where blood flow typically increases by five or ten percent.

One of the most famous cases of Synesthesia is that described in A.R Luria's book TThe Mind of a Mnemonist. Where he discusses his dealings over 30 years with 'S', a man who had various forms of synesthesia that he used in conjunction with memory techniques to enable him to remember anything he encountered with explicit detail, and for any length of time. Luria would test him out of the blue on material that they had covered 15 years previously, and not only would 'S' remember the pertinent information. He would also remember what Luria was wearing, the weather and the conversation on the day. The key to his abilities seemed to be that using his synesthesia he would create vivid visual images. This meant that he simply replayed back scenes like a movie and observed what occurred. It does have to be said though that in some ways this ability did handicap him. He found it difficult to read because the words would dissolve into images, and also it meant that forgetting unpleasant events became very difficult because they seemed to be literally ingrained into his mind. Nevertheless, it is interesting to note that most people who experience synesthesia also describe themselves as having excellent memories.

The beauty of synesthesia is that it gives us a window to a world of new possibilities in brain research, and also poses questions as to the nature of perception and reality. How we engage with the world around us, and whether that is necessarily the way that others do. It peeks at what it is to be human and have a continually altering idea of our own consciousness, and also makes us question how language structures emerge, and also the mechanisms by which our senses interact. And as the medical technology that can detect differences and nuances in brain chemistry and structure improves. We are left with the tantalising prospect of understanding how synesthesia works, in order not only to answer some of these fundamental questions, but also to learn how to use that knowledge to better ourselves.

Copyright - Stuart Brown