title: Frontal-posterior theta oscillations reflect memory retrieval during sentence comprehension.
abstract: Successful working-memory retrieval requires that items be retained as distinct units. At the neural level, it has been shown that theta-band oscillatory power increases with the number of to-be-distinguished items during working-memory retrieval. Here we hypothesized that during sentence comprehension, verbal-working-memory retrieval demands lead to increased theta power over frontal cortex, supposedly supporting the distinction amongst stored items during verbal-working-memory retrieval. Also, synchronicity may increase between the frontal cortex and the posterior cortex, with the latter supposedly supporting item retention. We operationalized retrieval by using pronouns, which refer to and trigger the retrieval of antecedent nouns from a preceding sentence part. Retrieval demand was systematically varied by changing the pronoun antecedent: Either, it was non-embedded in the preceding main clause, and thus easy-to-retrieve across a single clause boundary, or embedded in the preceding subordinate clause, and thus hard-to-retrieve across a double clause boundary. We combined electroencephalography (EEG), scalp-level time-frequency analysis, source localization, and source-level coherence analysis, observing a frontal-midline and broad left-hemispheric theta-power increase for embedded-antecedent compared to non-embedded-antecedent retrieval. Sources were localized to left-frontal, left-parietal, and bilateral-inferior-temporal cortices. Coherence analyses suggested synchronicity between left-frontal and left-parietal and between left-frontal and right-inferior-temporal cortices. Activity of an array of left-frontal, left-parietal, and bilateral-inferior-temporal cortices may thus assist retrieval during sentence comprehension, potentially indexing the orchestration of item distinction, verbal working memory, and long-term memory. Our results extend prior findings by mapping prior knowledge on the functional role of theta oscillations onto processes genuine to human sentence comprehension.
authors.affiliation: Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany. Electronic address: lmeyer@cbs.mpg.de.
authors.forename: Lars
authors.initials: L
authors.lastname: Meyer
authors.affiliation: Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Maren
authors.initials: M
authors.lastname: Grigutsch
authors.affiliation: Department of English and Linguistics, Johannes Gutenberg University, Mainz, Germany.
authors.forename: Noura
authors.initials: N
authors.lastname: Schmuck
authors.affiliation: Neuroscience of Language Laboratory, New York University, New York, NY, USA.
authors.forename: Phoebe
authors.initials: P
authors.lastname: Gaston
authors.affiliation: Department of Neuropsychology, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Friederici
mesh_terms: D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D032882:Comprehension / Q000502:physiology*; D004569:Electroencephalography; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D057567:Memory, Long-Term / Q000502:physiology; D008570:Memory, Short-Term / Q000502:physiology; D011939:Mental Recall / Q000502:physiology*; D010296:Parietal Lobe / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D013702:Temporal Lobe / Q000502:physiology; D013826:Theta Rhythm; D055815:Young Adult
keywords: Sentence comprehension; Source localization; Theta oscillations; Time–frequency analysis; Verbal working memory