Within-subject design reveals converging cortical regions for orthographic, phonological and semantic processing in Chinese reading

Abstract

A meta-analysis on 26 fMRI studies reveals that the activation for orthographic, phonological and semantic processing of Chinese characters converges at the left middle/inferior frontal gyrus (BA 46/9), left mid-fusiform gyrus (BA 19/37) and left superior parietal lobule (BA 7), while diverges at the left inferior parietal lobule (BA 40), inferior frontal gyrus (BA 44/45/47) and the right mid-fusiform (Wu, Ho & Chan, 2012). However, as the design of the reading tasks targeting the same process can vary substantially in a meta-analysis, the patterns of convergence or divergence could be obscured by factors such as different baseline tasks and response modality. To tackle these issues, we devised a within-subject design using three character reading tasks for the respective reading processes. Thirty-one native Mandarin speakers were recruited in Beijing and scanned with a Siemens Prisma 3T scanner at Peking University. To investigate orthographic processing, a component matching task was used. Two characters appeared on the screen simultaneously and participants judged whether they share the same component / radical. A line judgement task in which participants judged whether two line patterns were identical served as the baseline task. The phonological and semantic tasks were designed similarly but participants judged whether the two characters were homophones and synonyms respectively. A font-size judgement task served as the baseline task for these two reading tasks. The visual complexity of the characters, indicated by the number of strokes, and their frequency were controlled across the three tasks. To match the baseline task across the three tasks, 23 participants returned on another day and performed the same reading tasks with an interchanged baseline task. Conjunction analysis and paired t-test were used to identify the convergent and divergent regions of activation among the three tasks. Preprocessing and statistical analysis were performed with SPM12. The contrast maps of individual tasks revealed that the activation followed the same general patterns despite a change in the baseline task, so only the analysis of the first scanning session will be reported. Activations in typical regions responsible for Chinese character reading, such as the left middle frontal gyrus, left mid-fusiform gyrus and left superior parietal lobule were found in the conjunction analysis. Interestingly, the ventral portion of the middle frontal gyrus (Exner’s area, BA 6), which is less frequently reported and responsible for converting orthographic representation into motor sequence specific for writing (Roux et al., 2009), was also commonly activated. Pair t-tests showed that bilateral fusiform gyrus (BA 19/37) and superior bilateral lobule activated more strongly during the orthographic component matching task than the other tasks, while semantic processing uniquely recruited the inferior frontal gyrus (BA 45/47). Apart from minor deviations in activation sites, orthographic, phonological and semantic processing in Chinese reading share a largely similar brain circuit. Common activations in the Exner’s area point to the intertwined relationship of reading and writing in Chinese (Tan et al., 2005). Further investigation on the connectivity among these regions may reveal a deeper distinction among the cognitive mechanisms of the three reading processes.