EFFECTS OF SYNTACTIC STRUCTURE AND PROPOSITIONAL NUMBER ON PATTERNS OF REGIONAL CEREBRAL BLOOD-FLOW

Positron emission tomography (PET) was used to determine regional cere bral blood flow (rCBF) as a function of the syntactic form and proposi tional density of sentences. rCBF increased in the left pars opercular is, part of Broca's area, when subjects processed syntactically more c omplex sentences. There were no differences in rCBF in the perisylvian association cortex traditionally associated with language processing when subjects made plausibility judgments about sentences with two pro positions as compared to sentences with one proposition, but rCBF incr eased in infero-posterior brain regions. These results suggest that th ere is a specialization of neural tissue in Broca's area for construct ing aspects of the syntactic form of sentences to determine sentence m eaning. They also suggest that this specialization is separate from th e brain systems that are involved in utilizing the meaning of a senten ce that has been understood to accomplish a task.