Colours of the mind

New Scientist, 21 May 2007

Well, now I know the truth. Synaesthetes like me - people who can't help but conjure a colour when they encounter a letter or number or word - have weird connections in their brains.

"Abnormal" was the word used by Romke Rouw, the researcher at the University of Amsterdam who found the connections. But with new research suggesting synaesthesia occurs in about 1 in every 20 of us, it may not be quite as rare a trait as we synaesthetes have long believed. (You can test whether you have the trait on this site).

The idea that synaesthetes have "crossed wires" has been floating around for a while. It didn't go without notice that an area of brain that is involved in the perception and categorisation of visual stimuli, the fusiform gyrus, is located not far from an area that specialises in colour. And sure enough, using a sophisticated variation of MRI called "diffusion tensor imaging", Rouw and her team have now shown that there really is hyperconnectivity in these (and a few other) areas (see Nature Neuroscience).

There are all sorts of different kinds of synaesthetes and people who see their letters and numbers in colour are just a common subset. This diagram shows what other researchers say are frequent letter-colour associations - although most of them are off enough to make me feel physically ill.

Interestingly, the researchers were able to distinguish subsets within this subset: people who simply see their colours in their mind's eye appeared to have fewer hyperconnections than those who projected their colours out onto the world.

What's so wonderful about synaesthesia is that it's one of the few neurological quirks that causes absolutely no harm, yet might be able to illuminate a great deal about the brain.