Syntactic and thematic constraint effects on blood oxygenation level dependent signal correlates of comprehension of relative clauses.

The effects of plausibility of thematic role assignment and syntactic structure on blood oxygenation level dependent (BOLD) signal were studied using event-related functional magnetic resonance imaging by orthogonally varying syntactic structure (subject-vs. object-extracted relative clauses) and the plausibility of nouns playing thematic roles (constrained vs. unconstrained sentences) in a plausibility judgment task. In plausible sentences, BOLD signal increased for object-compared to subject-extracted clauses in unconstrained sentences in left middle temporal and left inferior frontal areas, for this contrast in constrained sentences in left middle temporal but not left inferior frontal areas, and for constrained subject-extracted sentences compared to unconstrained subject-extracted sentences in the left inferior frontal gyrus and the left dorsolateral prefrontal cortex. We relate these areas of activation to the assignment of the syntactic structure of object-compared to subject-extracted structures and the process of checking which thematic roles activated in the course of processing a sentence are licensed by the syntactic structure of the sentence.