Active maintenance of sentence meaning in working memory: evidence from EEG coherences.

The active maintenance of sentence meaning in working memory was investigated using event-related electroencephalogram (EEG) coherences. Participants read a sentence, retained it for 2.5 s, and then verified a statement about its meaning. The sentences contained either three semantically related nouns or unrelated nouns and started either with a what phrase (WH sentences) or not (non-WH sentences), imposing either a high or low demand on verbal working memory. Comprehension accuracy showed an interaction of semantic relatedness and sentence type due to the presence of a relatedness effect (lower accuracy in the unrelated condition) in WH sentences but not in non-WH sentences. During the post-sentence retention interval, EEG coherences also displayed this interaction of relatedness and sentence type. A semantic relatedness effect was obtained in the WH sentences (high demand) but not in the non-WH sentences (low demand). In addition, compared to a pre-sentence baseline and sentence presentation, coherences increased in the 10-14 Hz band during retention and decreased in the 4-6 Hz band. These coherence changes spanned prefrontal and posterior brain regions, possibly reflecting increased synchronization in projection loops between attention control systems in prefrontal cortex and activated meaning representations in semantic memory in posterior cortex. These findings suggest that short-term retention of the meaning of a sentence involves active maintenance in a capacity-limited working memory, accompanied by a heightened inner direction of attention after sentence presentation.