Brain Areas Involved in Tactile Letter Recognition (graphesthesia)

Kim, Kwang Ki; Woo, Sung Ho; Lee, Kyoung Min

Abstract

BACKGROUND
Graphesthesia is the ability to recognize letters or symbols via somatic sensation. We employed functional MRI to determine neurological substrates underlying this ability. We also designed a behavioral experiment to examine the relationship between graphesthesia and working memory. METHODS: Images were acquired in a 1.5T scanner from ten right-handed normal subjects while tactile stimulation was applied for either graphesthesia or simple sensation. Additional eight right-handed normal observers participated in the behavioral experiment where they performed a visuo-spatial or a verbal working memory task, simultaneously with graphesthesia. Overall performance times were measured to detect interference in the dual-task situations. RESULTS: Comparison between graphesthesia and simple sensory stimulation revealed activations at bilateral prefrontal, parietal and superior temporal cortices, regardless of the hand stimulated. The right parietal operculum was activated for both hand conditions, while the corresponding area in the left hemisphere was activated by right-hand stimulation only, suggesting a right-hemisphere dominance for graphesthesia. From the behavioral experiments, we observed that the visuo-spatial task, but not the verbal task, interfered with graphaesthesia. CONCLUSIONS: Taken together, these results suggest that the brain areas underlying the visuo-spatial sub-system of working memory are involved in graphesthesia and that some cognitive processes underlying graphesthesia are right-lateralized.