The role of the prefrontal cortex in sentence comprehension: an rTMS study

Using repetitive transcranial magnetic stimulation (rTMS), we investigated the role of the left and right dorsolateral prefrontal cortex (DLPFC) in sentence comprehension. Subjects were required to judge which of the two pictures correctly matched the meaning of active and passive semantically reversible sentences (subject-verb-object); the incorrect picture did not match the sentence in term of lexical items (semantic task) or agent-patient structure (syntactic task). The subjects performed the task while a series of magnetic stimuli were applied to the left or right DLPFC. When rTMS was applied to the left DLPFC, the subjects' performance was delayed only for the semantic task, while rTMS applied to the right DLPFC slowed the processing of syntactic information. The results of this experiment provide direct evidence of a double dissociation between the rTMS effects and the type of task, which may reflect a differential hemispheric involvement of working memory resources during sentence comprehension.