Neurophysiological investigation of idiopathic acquired auditory-visual synesthesia

Migraine in Synesthetes and Nonsynesthetes: A Prevalence Study

Synesthesia is a neurological condition in which an inducer stimulus in one sense leads to a concurrent percept in a second sense. The immune hypothesis of synesthesia links synesthesia to immune-related conditions such as migraine. More specifically, migraine with aura may be linked to grapheme-color synesthesia as both involve cortical hyperexcitability. In this study, 161 female synesthetes, and 92 female nonsynesthetes, completed an online questionnaire about synesthesia and migraine. We found no general link between migraine and synesthesia nor between migraine with aura and grapheme-color synesthesia. Exploratory analyses, however, showed that certain types of synesthetic inducer (non-linguistic visual experiences, scent, taste, emotion and personality) were associated with visual disturbances in headache among female participants, and touch as a concurrent was associated with migraine with aura. On the basis of our exploratory analyses, we hypothesize that specific subtypes of synesthesia are related to migraine. The relationship between these two conditions is likely to become clearer as research on the underlying causes of synesthesia and migraine progresses.

Cross-modal, bidirectional priming in grapheme-color synesthesia

Grapheme-color synesthetes perceive achromatic graphemes to be inherently colored. In this study grapheme-color synesthetes and non-synesthetes discriminated (1) the color of visual targets presented along with aurally presented digit primes, and (2) the identity of aurally presented digit targets presented with visual color primes. Reaction times to visual color targets were longer when the color of the target was incongruent with the synesthetic percept reported for the prime. Likewise, discriminating aurally presented digit targets took longer when the color of the prime was incongruent with the synesthetic percept for the target. These priming effects were absent in non-synesthetes. We conclude that binding between digits and colors in grapheme-color synesthetes can occur bidirectionally across senses. The results are in line with the idea that synesthesia is the result of linking inducing stimuli (e.g. digits) to synesthetic percepts (colors) at an abstract - supra-modal - conceptual level of processing.