This is a quote from Dr Julia Simner’s thought-provoking paper in the British Journal of Psychology about defining synaesthesia:
“To avoid this circular evidence of what synaesthesia is and is not, we might instead define synaesthesia in terms of it neurological basis, and then allow ourselves to consider what types of variants this synaesthesia might then include. If indeed the condition were defined by inherited atypical cross-talk, we might find synaesthesiae in unexpected places. For example, if an inherited predisposition for neurological hyper-association manifested itself, say, in the fronto-temporal language regions that mediate semantics, lexical-forms, and syntax (e.g., see Tyler & Marslen-Wilson, 2008, for review) what would this mean? It might mean we could find ‘synaesthetic’ individuals with unusually strengthened connections in spoken language processing.”
I happened across this picture that is apparently from The Human Connectome Project, or at least from a paper by Liza Gross that was published in PLoS Biology in 2008: http://www.abc.net.au/radionational/programs/allinthemind/the-human-connectome/3706910 I’m guessing that the coloured larger blobs represent the most connected hubs in the brain, and I’m guessing these bits would be made of white matter? I know that there is one type of synaesthesia that is associated with some kind of functional enhancement of white matter, and in general, synaesthesia is thought to be due to hyperconnectivity in the brain, which I guess might mean that it operates the most in regions of the brain that are the most connected? Well, looking at the picture with the red and pink blobs, it seems as though the parts of the brain that are the most connected are towards the rear of the brain, maybe the parietal, occipital and part of the temporal lobes, with most of the frontal lobe and Broca’s area (important in language processing) left pretty much out of the loop. So I’ve got to wonder how realistic is Dr Simner’s theoretical idea of a type of person who is especially articulate due to a hidden type of synaesthesia based in the “fronto-temporal language regions”. I certainly do think it is probable that there are non-obvious and undiscovered types of synaesthesia linking brain functions that researchers haven’t already known to be hyperconnected, but I suspect that researchers will also find that synaesthesia is more likely in some regions of the brain than others. I’ve long ago noticed that most types of synaesthesia that are known to science (and to me) involve the sense of sight in one way or another (scenes, colours, shapes, faces, visual-spatial landscapes etc), and where is vision processed in the brain? At the rear, where so many of those red blobs are found.
Simner, J. (2012), Defining synaesthesia. British Journal of Psychology, 103: 1–15. doi: 10.1348/000712610X528305 Article first published online: 11 MAR 2011 DOI: 10.1348/000712610X528305 http://onlinelibrary.wiley.com/doi/10.1348/000712610X528305/full
Gross L (2008) From Structure to Function: Mapping the Connection Matrix of the Human Brain. PLoS Biol 6(7): e164. doi:10.1371/journal.pbio.0060164 http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0060164
Human Connectome Project http://www.humanconnectomeproject.org/