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Neural mechanisms of synesthesia| old_uid | 4888 |
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| title | Neural mechanisms of synesthesia |
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| start_date | 2008/05/22 |
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| schedule | 16h |
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| online | no |
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| summary | Synesthesia is an unusual inherited condition in which stimulation in one modality can trigger extra sensations in an entirely separate modality. For example, individuals may experience vivid colors or tastes when they hear particular sounds, or feel unusual tactile sensations against the skin when they taste specific foodstuffs. Ramachandran and Hubbard (2001) proposed that grapheme-color synesthesia might be due to a genetic mutation that leads to incomplete pruning between adjacent grapheme selective regions and color sensitive region V4 (the "cross-activation" theory). Here, I review our earlier behavioral and neuroimaging investigations, and subsequent research which has suggested specific neural correlates for other forms of synesthesia. Some examples suggest that the cross-activation theory can be successfully extended to other forms of synesthesia. For example, Hubbard et al. (2005) have suggested that number forms may arise from cross-activation between numerical and spatial regions in the parietal cortex, Simner and Hubbard (2006) have suggested that ordinal linguistic personification arises from cross-activation between ordinal sequence and personality representations in the inferior parietal lobule, and Ward, Simner, Ayeung (2003) have suggested that lexical-gustatory synesthesia from cross-activation between lexical representations in the superior temporal sulcus and gustatory cortex in the insula. However, other forms of synesthesia may require a more complex model. Given that even with auditory input, synesthetic colors are often sensitive to graphemic representations, we suggest that auditory word to color synesthesia may arise through a two stage process, in which auditory sounds activate grapheme regions, which in turn activate V4. Currently no such models exist for pure tone-color synesthesia or emotion-color synesthesia, making these interesting future test-cases of the theory. Based on its success in explaining many forms of synesthesia, we suggest that anatomically constrained cross-activation may constitute a Grand Unified Theory of Synesthesia. |
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| responsibles | Cousineau, Barthelme |
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