The role of the left prefrontal cortex in sentence-level semantic integration.

Whether left inferior frontal gyrus (LIFG) activation during sentence comprehension reflects semantic integration or domain-general cognitive control remains unclear. To address this issue, 26 participants were presented with sentences word by word during fMRI scanning and were asked to perform two semantic tasks, one explicit (semantic congruency judgment) and one implicit (font size judgment). In the two language tasks, semantic integration load was parametrically manipulated with high cloze, low cloze and semantically violated sentences. Participants also performed a classical Stroop task during scanning. Conjunction analysis of the explicit and implicit tasks revealed two regions in left inferior frontal gyrus associated with semantic integration load: one anterior region (aIFG) and one posterior region (pIFG). However, only the pIFG region was also activated during the Stroop task. These results indicate that different regions in the LIFG play different roles in semantic integration, with aIFG more important for domain-specific processing and pIFG more important for domain-general cognitive control.