Poster A21, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Investigating the role of inter-hemispheric communication in age-related increase in right-hemisphere P600 grammaticality effect: a combined ERP and DTI study
Po-Heng Chen1, Jen-Shiang Wong1, Wan-Ting Lin1, Wen-Yih Isaac Tseng1, Joshua Oon Soo Goh1, Chia-Lin Lee1;1National Taiwan University
Syntactic processing is strongly lateralized toward the left hemisphere (LH) in young right-handers but tend to additionally engage the right hemisphere (RH) with age. The present study investigated how this age-related bilateralized syntactic processing is moderated by inter-hemispheric communication. Event-Related Potentials to grammatical or ungrammatical two-word pairs (a centrally-presented syntactic cue followed by a target word presented to either visual field) were collected from 35 right-handed healthy older adults and were time locked to the laterally-presented target word. Consistent with the aging literature, bilateral syntactic processing was observed, with significant P600 grammaticality effects with both visual-field (VF) presentations. All participants underwent behavioral tasks to measure inter-hemispheric inhibition and coordination. Results from the bilateral flanker task, in which the target arrow and the distracting arrow were presented in different VF and either congruent or incongruent with regard to their direction, showed reliable flanker effect regardless of whether the distractor was presented to which VF, suggesting symmetrical inter-hemispheric inhibition in older adults. In addition, older adults performed better in the word matching task when two semantically related or unrelated words were presented bilaterally than unilaterally, suggesting a trend of benefits from cross-hemispheric coordination. However, individual differences in these tasks did not correlate with the magnitudes of the RH P600 effect. Finally, for a subset of 20 participants, diffusion tensor imaging (DTI) data were obtained and microstructural tissue integrity of the corpus callosum (CC) was estimated with fractional anisotropy (FA). Extant neuroimaging data suggest that the anterior and posterior part of the corpus callosum (CC), genu and splenium, may affect the extent of functional lateralization differentially. While weaker structural integrity of genu is associated with greater RH activity, implicating a role of inter-hemispheric inhibition for genu, larger size of splenium is associated with better performance in demanding language tasks, implicating a role of inter-hemispheric excitation for splenium. Hence, examining the associations between the microstructure of genu and splenium and RH P600 effects could help clarify the modulating factors for the additional RH syntactic processing. Our results showed that FA of the splenium was predictive of the RH P600 effects, with larger FA values associated with larger P600 effects. Correlation between FA of the genu and RH P600 effect, however, was not reliable. Together, this study replicated bilateral P600 grammaticality effect in healthy older adults. We did not observe evidence supporting the relation between reduced inter-hemispheric inhibition and increased RH syntactic processing in these older adults. However, our results suggest that age-related additional syntactic processing in the non-dominant RH may be associated with the cross-callosal excitation via the splenium.
Themes: Syntax, Control, Selection, and Executive Processes
Method: Electrophysiology (MEG/EEG/ECOG)