Abstract
Gustatory forms of synesthesia involve the automatic and consistent experience of tastes that are triggered by non-taste related inducers. We present a case of lexical-gustatory and sound-gustatory synesthesia within one individual, SC. Most words and a subset of non-linguistic sounds induce the experience of taste, smell and physical sensations for SC. SC's lexical-gustatory associations were significantly more consistent than those of a group of controls. We tested for effects of presentation modality (visual vs. auditory), taste-related congruency, and synesthetic inducer-concurrent direction using a priming task. SC's performance did not differ significantly from a trained control group. We used functional magnetic resonance imaging to investigate the neural correlates of SC's synesthetic experiences by comparing her brain activation to the literature on brain networks related to language, music, and sound processing, in addition to synesthesia. Words that induced a strong taste were contrasted to words that induced weak-to-no tastes (“tasty” vs. “tasteless” words). Brain activation was also measured during passive listening to music and environmental sounds. Brain activation patterns showed evidence that two regions are implicated in SC's synesthetic experience of taste and smell: the left anterior insula and left superior parietal lobe. Anterior insula activation may reflect the synesthetic taste experience. The superior parietal lobe is proposed to be involved in binding sensory information across sub-types of synesthetes. We conclude that SC's synesthesia is genuine and reflected in her brain activation. The type of inducer (visual-lexical, auditory-lexical, and non-lexical auditory stimuli) could be differentiated based on patterns of brain activity.
Highlights
Synesthesia refers to the experience of cross-modal sensory mappings, in which the corresponding external stimulation of the additional perceived sense is absent
SC reported experiencing synesthesia her whole life; that it is induced by hearing people speak, speaking herself, reading and “inner” speech; the concurrent sensations are as complex as real tastes or smells, which can be pleasant and unpleasant; the concurrent sensations are felt on the tongue, mouth and throat; food words taste like the foods that they describe (Pierce, 1907; Ward and Simner, 2003; Gendle, 2007; Richer et al, 2011)
We present SC’s activation as a supplement to Jones et al (2011) so that it may serve as a useful reference for future functional magnetic resonance imaging (fMRI) studies on such rare cases of lexical-gustatory synesthesia
Summary
Synesthesia refers to the experience of cross-modal sensory (and conceptual) mappings, in which the corresponding external stimulation of the additional perceived sense is absent. For a summary of reported cases of synesthesia related to taste, we refer the reader to Ward and Simner (2003). In lexical-gustatory synesthesia, the synesthetic percept of taste is typically as complex as veridical taste (e.g., potatoes with gravy), while generic tastes (e.g., bitter, sweet) are notably absent (Pierce, 1907; Ward and Simner, 2003; Richer et al, 2011). As is the case with all sub-types of synesthesia, individual differences in the specific experiences are reported and multiple types of synesthesia may co-exist within one individual (e.g., Beeli et al, 2005; Hänggi et al, 2008)
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