In a provocative review paper just published, French neuroscientists Jean-Michel Hupé and Michel Dojat question the assumption that synesthesia is a neurological disorder.
In synesthesia, certain sensory stimuli involuntarily trigger other sensations. For example, in one common form of synesthesia, known as ‘grapheme-color‘, certain letters are perceived as allied with, certain colors. In other cases, musical notes are associated with colors, or smells.
The cause of synesthesia is obscure. Many neuroscientists (including Hupé and Dojat) have searched for its brain basis. One theory is that it’s caused by ‘crossed wires’ – abnormal connections among the sensory processing areas of the brain.
But – according to Hupé and Dojat – the studies to date have failed to find anything, and the only conclusion we can draw from these studies is that “the brains of synesthetes are functionally and structurally similar to the brains of non-synesthetes.”
To reach this conclusion they reviewed 19 studies of brain grey and white matter structure (using MRI and DWI) in synesthetes, comparing them to people without the condition. They conclude
We did not find any clear evidence of structural brain alterations in synesthetes, either local differences or differences in connectivity, at least when considering the data with no a priori…
More structural results exist in favor of the role of the parietal cortex in synesthesia. However… there was no consistency across studies about the precise anatomical location of which part of the parietal cortex was supposed to be involved.
http://blogs.discovermagazine.com/neuro ... -disorder/
21 Apr 2015, 11:15 pm
