Functional connectivity of the left inferior frontal gyrus during semantic priming

Recent applications of computationally calculated word co-occurrences allowed the prediction of left inferior frontal gyrus (LIFG) activation during semantic word processing. Hence, an interactive activation model, the associative read-out model (AROM), utilizes co-occurrences in its semantic processing layer and proposes connectivity from the LIFG along the ventral visual stream. Direct empirical evidence for its connectivity assumptions is so far missing, however. In this study, we employed psychophysiological interaction analysis on the neuroimaging data of a semantic priming experiment, targeting the LIFG as main region to resolve semantic conflicts. We further manipulated the prime and target word by co-occurrence-based direct association and semantic similarity in a full-factorial design. At a low semantic similarity, we observed increased functional connectivity of the LIFG to the fusiform gyrus, the hippocampus, the anterior cingulate cortex and the orbitofrontal cortex, indicating a connective pattern analogous to the semantic layer of the AROM. Surprisingly, a low (compared to a high) direct association showed no difference in brain activation, which raises the question about the diverging cognitive processes of the two priming types.