Monday July 09 2007
CEA
synaesthesia, or when images come by surprise…
Nature Neuroscience (2007) 10 : 671-672 ; Current psychiatry reports (2007) 9 : 193-199
CEA
To gain further insight into the various forms of synaesthesia and the cognitive phenomena involved
“Wednesday, a bright pink word”: Associating a word to a colour is not just poetry, it is a phenomenon called synaesthesia, from the Greek syn, meaning with, and aesthesis, meaning sensation, a neurological condition wherein two or more senses become associated.
For instance, there is a well-known form of synaesthesia known as ‘grapheme-colour synaesthesia’ where all the alphanumeric characters (letters and digits) can be perceived in colours. In another form, called number form synaesthesia, the numbers are automatically and involuntarily associated with positions in space.
Synaesthesia is as prevalent as 1 in 23 persons. It is a little-known phenomenon, studied by fewer than 5 researchers in France and only fifty or so across the world.
Working at NeuroSpin, in the Institute of Biomedical Imaging (CEA-I²BM), Edward Hubbard has just published two articles focusing on the subject. One, published in Nature NeuroScience (2007, 10: 671-672) and titled ‘A real red-letter day’, provides further analysis of the work published by R. Rouw and H.S. Scholte, while the other, published in Current Psychiatry Reports (2007,9: 193-199) and titled ‘Neurophysiology of synaesthesia’, provides an update review on the various forms of synaesthesia studied.
Research into synaesthesia has boomed over the last decade. As researchers delved deeper into the phenomenon, they revealed that these synaesthetic colours have consequences on perception, thus demonstrating the reality of the phenomena involved. Neuroimaging studies (by functional fMRI) have shown that synaesthetes who see stimuli inducing colour-based perceptions actually display activations in the brain regions that process colour, suggesting that synaesthesia is due to co-activation of adjacent brain regions involved in processing colour and processing number (highlighted in green and red in the illustration).
Edward Hubbard is currently focusing his research into number-form synaesthesia. The results of a 2007 study led at the Frédéric Joliot Hospital Centre and involving a subject population of 20 volunteers (10 synaesthetes and 10 controls) are scheduled to be published soon. E. Hubbard designed this study to show that other forms of synaesthesia are due to similar co-activation mechanisms in the regions involved in processing quantity and spatial awareness (highlighted in blue and red in the illustration).
Further perspectives at NeuroSpin? To continue the high-field fMRI experiments using better spatial resolutions in order to more clearly highlight the neurophysiological roots of these phenomena, and by extension, the bases of conscious experience.
For synaesthetes associating numbers with colours, the figures are not black but green for 5 and red for 2, making them faster at differentiating twos from fives.