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Neural correlates of the processing of linear and hierarchical artifical grammar rules: Electrophysiological and neuroimaging studies

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Bahlmann,  Jörg
Department Neuropsychology, MPI for Human Cognitive and Brain Sciences, Max Planck Society;

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Bahlmann, J. (2007). Neural correlates of the processing of linear and hierarchical artifical grammar rules: Electrophysiological and neuroimaging studies. PhD Thesis, Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0010-CACE-F
Abstract
The aim of the dissertation presented here was to investigate neural correlates of the processing of two different types of artificial grammar rules. The rules differed in complexity. The Finite State Grammar (FSG) rule was specified by local adjacent probabilities. In contrast, the Phrase Structure Grammar (PSG) rule generated hierarchical dependencies via center-embeddings. Electrophysiological changes were recorded using event-related brain potentials (ERPs) and hemodynamic changes were measured applying functional Magnetic Resonance Imaging (fMRI). Within three experiments the structures of the rules were systematically changed. The processing of the two artificial grammar types revealed differences in the late positivity on violations of the structures. The amplitude of the late positivity varied as a function of the position of a violation of the sequence in the PSG rule. In contrast, no changes of the amplitude of the varying violation positions of the FSG were found. FMRI results revealed an increased activity in Broca’s area on violations of the PSG, but not of the FSG. Additionally, the frontal operculum was associated with anomalies independent of the rule type. Moreover, the direct contrast of PSG sequences versus FSG sequences also correlated with an increased hemodynamic response function in Broca’s area and it’s right hemispheric homologue. The chunking of the elements of the artificial structure and the maintenance of the particular element in working memory until the matching category occurred describes the long distance dependencies of the PSG structure at hand. This process was correlated with activity in Broca’s area in the present work. Hence, Broca’s area could be associated with working memory demands during the processing of artificial hierarchical structures. These finding could be interpreted as a potential key role of Broca’s area in a network of the processing of hierarchical structures.