Selective response to letter categorization within the left fusiform gyrus

Abstract

Neuroimaging studies that look at reading processes using words, pseudowords, nonwords and letters frequently report specific left fusiform gyrus (BA37) activations. In the present study, we examined fMRI signal variations within the left and right BA37 for paired Latin letters, Korean letters and geometrical figures in discrimination and categorization tasks. Data of Pernet et al. (Pernet, C., Franceries, X., Basan, S., Cassol, E., Démonet, J.F., Celsis, P., 2004. Anatomy and time course of discrimination and categorization processes in vision: an fMRI study. NeuroImage 22, 1563–1577) were re-analyzed using a ROI methodology that highlights the selective response of the left BA37 to Latin letter categorization. First, differences according to stimulus type were observed for the categorization task only. Second, we found weaker activation for Latin letter categorization than for both geometrical figure and Korean letter categorization. Third, only Latin letter categorization elicited as left-sided activation, although the direct comparison between regions did not demonstrate a significant difference. These data suggest that the left fusiform gyrus sustains access to letter representations in memory; and results are discussed with reference to the relationship between letter categorization and word recognition and to selective vs. specific (i.e. task-independent) neural response.