Grapheme-color synesthesia in patients with epilepsy: A pilot study

Synesthesia is a condition in which the stimulation of one sensory modality triggers unusual experiences in a second sensory modality such as colors or shapes. Synesthesia has been linked to specific conditions such as autism spectrum disorder, although the mechanisms underlying synesthesia remain largely unclear.

This pilot study aimed to investigate the prevalence of grapheme-color synesthesia (GCS) in patients with epilepsy and to characterize the epilepsy features associated with GCS experiences.

Participants were asked whether they reported experiences suggesting GCS. Those reporting GCS underwent a standard online consistency and congruency battery test (http://www.synesthete.org). Epilepsy features, electroencephalogram (EEG) findings, and magnetic resonance imaging (MRI) findings were collected and analyzed.

Of the 40 study participants, 21 reported GCS experiences and 3 (7.5 %) resulted synesthetes from the battery test. Analysis of the test results showed that participants with focal seizures had lower median consistency scores (indicating they were less consistent in their color assignments) and higher congruency scores (indicating they were more accurate in quickly identifying matching color and letter/number combinations) compared to patients with generalized-onset seizures (2.9 and 51.4 respectively; p = 0.006, p = 0.001). Participants with non-motor seizures had lower median consistency scores (1.1) and higher congruency scores (79.2) compared to patients with motor seizures (2.8 and 52.8, respectively; p = 0.011, p = 0.036).

GCS may be more prevalent in patients with epilepsy than the general population. Focal and non-motor seizures may be associated with predisposition to GCS. Further larger scale studies are needed to confirm and expand these observations.