Activation of Broca's area by syntactic processing under conditions of concurrent articulation.

Regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) when 11 subjects made plausibility judgments about written sentences that varied in their syntactic complexity. While making their judgments, subjects uttered the word "double" aloud at a rate of one utterance per second to inhibit their ability to rehearse the sentences. Blood flow increased in Broca's area when subjects made judgments about the more complex sentences. This result replicates and extends previous findings that blood flow increases in this region when subjects process complex syntax under no interference conditions. The results of this experiment provide strong evidence that the increase in blood flow seen in Broca's area in association with processing syntactically complex structures is not due to subvocal rehearsal of those structures, but rather results from processing syntactic forms themselves.