In 1880 Francis Galton, a cousin of Charles Darwin and a celebrated scientist himself, published a paper in Nature on the intriguing phenomenon of synesthesia. Synesthesia, from the Greek roots syn, meaning “together”, and aesthesis, or “perception”, is a condition in which people experience the blending of two or more senses, perhaps because two separate areas of the brain elicit activity in each other. Even though scientists have known about synesthesia since Galton times, for lacking in brain knowledge and subjective nature of the phenomenon, it has often been considered as fakery, an artifact of drug use or a mere curiosity.

In the new millennium beginning, Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California in San Diego and his fellow student Edward Hubbard (now postdoctoral fellow at INSERM) among others, began to uncover brain processes that could account for synesthesia (Psychophysical Investigations into the Neural Basis of Synaesthesia. Proceedings of the Royal Society of London, B, 268, 979-983, 2001).

Perhaps one person in 200 experience the phenomenon, which can occur in about 50 different types. In a common form of synesthesia, looking at a number can evoke a colour. It has been demonstrated that brain areas that normally don’t interact when processing numbers or colours do activate one another in synesthesia (Hubbard et al., Individual Differences among Grapheme-Color Synesthetes: Brain-Behaviour Correlations. Neuron 45 (6), 975-985, 2005). In one rare kind each letter is associated with male or female sex.

Synestesia is much more common in creative people than in the general population, and it seems more frequent in women than men. As the condition runs in families, neurogenetic studies might provide relevant insights into molecular differences from normal people.

Studying mechanisms involved in synesthesia Ramachandran, Hubbard and their colleagues are also learning about how the brain in general processes sensory information and uses it to make abstract connections between seemingly unrelated inputs. For that they consider synesthesia a window into the nature of thought.


BM&L-December 2005