Brain activation modulated by the comprehension of normal and pseudo-word sentences of different processing demands: a functional magnetic resonance imaging study

Recent data from lesion and brain imaging studies have questioned the well-established assumption of a close functional-anatomic link between syntax and Broca's area and semantics and Wernicke's area. In the present study we used functional magnetic resonance imaging (fMRI) to investigate the neuroanatomical correlates of semantic and syntactic functions and possible interdependencies between the related brain systems. In a completely crossed design we varied syntactic processing demands (easy vs difficult to process word order sequences) and the meaningfulness of sentences (real- vs pseudo-word sentences). In comparison to a backward speech condition we found an activation of the left perisylvian region, including the left inferior frontal cortex and the left superior and middle temporal gyri. Semantic in contrast to pseudo-word sentences elicited a stronger activation in both the anterior and the posterior perisylvian cortex. Syntactic difficulty had its strongest effect within the left inferior frontal region and this effect was more pronounced for semantic than nonsemantic speech. These results suggest that semantic and syntactic language functions are mediated by partly specialized brain systems but that there nevertheless exists a substantial functional overlap of the involved brain structures.