Event-related fMRI reveals cortical sites involved in contextual sentence integration.
We examined the effects of difficulty of sentential integration on blood oxygenation level-dependent contrast changes. Difficulty of integration was operationalized as the degree to which sentence-final nouns matched the expectations generated by preceding context. Nine young adults read short sentence fragments (e.g., "The pilot flies.") which were completed by highly expected nouns (e.g., "the plane"), unexpected yet semantically legal nouns (e.g., "the kite"), nouns that violated the verbs' selection restriction rules (e.g., "the book"), and pseudowords (e.g., "the foop") and made quick lexical decisions on the sentence-final item. Overall, word completions resulted in higher changes in activation than pseudoword completions. The largest of those changes were observed in left angular and posterior middle temporal gyri, suggesting that despite the lexical nature of the task, word stimuli embedded in sentence contexts triggered integrative-semantic processes beyond a lexical level. A region-of-interest analysis in left inferior frontal and left posterior middle temporal areas revealed activation for both unexpected and anomalous completions when compared to expected completions. Thus, while the underlying processing mechanisms may differ, sentential integration appears similarly effortful for these two types of completions. Our findings are consistent with previous reports of local increases in activation as a function of (syntactic) complexity, while extending the findings to processing demands of semantic integration. Because of its sensitivity to changes in semantic congruence and the implicit nature of the task involved, we argue that the present paradigm is well suited to study patients with potential semantic deficits after brain damage.
Baumgaertner
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Cognitive Neuroscience Laboratory, Department of Neurology, University of Hamburg Medical School, D-20246 Hamburg, Germany. baumgaer@uke.uni-hamburg.de
Weiller
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Büchel
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D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007802:Language; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged