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Combined structural and functional imaging reveals cortical deactivations in grapheme-colour synaesthesia.



Subject Keywords: fMRI; VBM; Neuroscience; Cognitive Development/Processes;

Synaesthesia is a heritable condition in which particular stimuli generate specific
and consistent sensory percepts or associations in another modality or processing
stream. Functional neuroimaging studies have identified potential correlates of these
experiences, including, in some but not all cases, the hyperactivation of visuotemporal
areas and of parietal areas thought to be involved in perceptual binding. Structural
studies have identified a similarly variable spectrum of differences between synaesthetes
and controls. However, it remains unclear the extent to which these neural correlates
reflect the synaesthetic experience itself or additional phenotypes associated with
the condition. Here, we acquired both structural and functional neuroimaging data
comparing thirteen grapheme-color synaesthetes with eleven non-synaesthetes. Using
voxel-based morphometry and diffusion tensor imaging, we identify a number of clusters
of increased volume of gray matter, of white matter or of increased fractional anisotropy
in synaesthetes vs. controls. To assess the possible involvement of these areas in
the synaesthetic experience, we used nine areas of increased gray matter volume as
regions of interest in an fMRI experiment that characterized the contrast in response to
stimuli which induced synaesthesia (i.e., letters) vs. those which did not (non-meaningful
symbols). Four of these areas showed sensitivity to this contrast in synaesthetes but not
controls. Unexpectedly, in two of them, in left lateral occipital cortex and in postcentral
gyrus, the letter stimuli produced a strong negative BOLD signal in synaesthetes. An
additional whole-brain fMRI analysis identified 14 areas, three of which were driven
mainly by a negative BOLD response to letters in synaesthetes. Our findings suggest that
cortical deactivations may be involved in the conscious experience of internally generated
synaesthetic percepts.

Suggested citation:

NEWELL, FIONA; . () Combined structural and functional imaging reveals cortical deactivations in grapheme-colour synaesthesia. [Online]. Available from: [Accessed: 21st May 2019].


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