Spatiotemporal dynamics of argument retrieval and reordering: An fMRI and EEG study on sentence processing

In sentence processing, it is still unclear how the neural language network success-fully establishes argument-verb dependencies in its spatiotemporal neuronal dynamics. Previous work has suggested that the establishment of subject-verb and object-verb dependencies requires argument retrieval from working memory, and that dependency establishment in object-first sentences additionally necessitates argument reordering. We examine the spatiotemporal neuronal dynamics of the brain regions that subserve these sub-processes by crossing an argument reordering factor (i.e., subject-first versus object-first sentences) with an argument retrieval factor (i.e., short versus long argument-verb dependencies) in German. Using functional magnetic resonance imaging (fMRI), we found that reordering demands focally activate the left pars opercularis (Broca's area), while stor-age and retrieval demands activated left temporo-parietal (TP) regions. In addition, when analyzing the time course of fMRI-informed equivalent current dipole sources in the EEG at the subcategorizing verb, we found that activity in theTP-region occurs relatively early (40-180 ms), followed by activity in Broca's area (300-500 ms).These findings were matched by topographical correlation analyses of fMRI activations in EEG sensor space, showing that, in the scalp potential, TP-region activity surfaces as an early positivity and IFG activity as a later positivity in the scalp potential. These results provide fine-grained evidence for spa-tiotemporally separable sub-processes of argument retrieval and reordering in sentence processing.