Interaction between Brain Regions during Semantic Processing in Chinese Adults

Using functional magnetic resonance imaging (fMRI) and dynamic causal modeling (DCM) methods, we investigated the neural correlates of meaning processing in different brain regions and calculated the inter-connection among these regions during semantic judgments to visual Chinese characters. Twentyfive healthy Chinese adults were asked to indicate if character pairs were related in meaning. Experimental stimuli were character pairs that included semanticallyrelated and semantically-unrelated pairs. The behavioral results showed that reaction times were significantly faster for the related condition than the unrelated condition. fMRI analyses showed greater activation in left inferior frontal gyrus (IFG, BA 45, 47), left posterior middle temporal gyrus (MTG, BA 21) and left fusiform gyrus (FG, BA 37) for the related versus baseline condition, and in left inferior parietal lobule (IPL, BA 39, 40) for the related versus unrelated condition. Effective connectivity from DCM analyses showed modulatory effects from left inferior frontal gyrus to left posterior middle temporal gyrus, suggesting top-down influences of the frontal cortex on retrieval of semantic representations. Effective connectivity analyses also showed modulatory effects from left posterior middle temporal gyrus to left inferior frontal gyrus, suggesting the role of MTG on providing relevant associations in verbal semantic memory for IFG to perform retrieval. We also found significant modulatory effects from left fusiform gyrus to left posterior middle temporal gyrus, suggesting bottom-up orthographic influences on semantic representations. These findings suggest dynamic interaction between brain regions during semantic processing to written characters in Chinese adults.