Segregating the core computational faculty of human language from working memory

In contrast to simple structures in animal vocal behavior, hierarchical structures such as center-embedded sentences manifest the core computational faculty of human language. Previous artificial grammar learning studies found that the left pars opercularis (LPO) subserves the processing of hierarch...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 2009-05, Vol.106 (20), p.8362-8367
Main Authors: Makuuchi, Michiru, Bahlmann, Jörg, Anwander, Alfred, Friederici, Angela D
Format: Article
Language:English
Subjects:
Adult
Anatomy
Animal behavior
Biological Sciences
Brain Mapping
Connectivity
Criminal sentencing
Female
Frontal Lobe
Humans
Language
Language comprehension
Magnetic Resonance Imaging
Male
Memory
Memory - physiology
Nerve Fibers, Myelinated
Neural Pathways
NMR
Nuclear magnetic resonance
Relative clauses
Sentence structure
Syntactics
Temporal Lobe
Verbs
Words
Working memory
Young Adult
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Summary:In contrast to simple structures in animal vocal behavior, hierarchical structures such as center-embedded sentences manifest the core computational faculty of human language. Previous artificial grammar learning studies found that the left pars opercularis (LPO) subserves the processing of hierarchical structures. However, it is not clear whether this area is activated by the structural complexity per se or by the increased memory load entailed in processing hierarchical structures. To dissociate the effect of structural complexity from the effect of memory cost, we conducted a functional magnetic resonance imaging study of German sentence processing with a 2-way factorial design tapping structural complexity (with/without hierarchical structure, i.e., center-embedding of clauses) and working memory load (long/short distance between syntactically dependent elements; i.e., subject nouns and their respective verbs). Functional imaging data revealed that the processes for structure and memory operate separately but co-operatively in the left inferior frontal gyrus; activities in the LPO increased as a function of structural complexity, whereas activities in the left inferior frontal sulcus (LIFS) were modulated by the distance over which the syntactic information had to be transferred. Diffusion tensor imaging showed that these 2 regions were interconnected through white matter fibers. Moreover, functional coupling between the 2 regions was found to increase during the processing of complex, hierarchically structured sentences. These results suggest a neuroanatomical segregation of syntax-related aspects represented in the LPO from memory-related aspects reflected in the LIFS, which are, however, highly interconnected functionally and anatomically.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.0810928106