Lateralization as a Symphony: Joint Influence of Interhemispheric Inhibition and Transmission Delay on Brain Asymmetry and Syntactic Processing

Abstract

The present study investigated the roles of cross-hemispheric communication in promoting left-lateralization of syntactic processing in the brain. Fifty-six young right-handers without familial sinistrality background underwent a divided visual field ERP grammaticality judgment experiment to assess syntactic responses from each hemisphere. Two behavioral tasks--bilateral flanker task and bilateral word-association task, were used to assess cross-hemispheric inhibition and transmission delays. The grand average ERP data showed a significant unilateral P600 grammaticality effect in the left hemisphere only. However, individual variations in the P600 responses were observed in both hemispheres. Results of correlational analyses showed that larger LH P600 effects were associated with slower inter-hemispheric transmission, and that smaller right hemisphere (RH) P600 effects were associated with more effective LH-on-RH inhibition. These results yielded support for both the callosal distance and inhibition hypotheses for language lateralization and demonstrated that different aspects of cross-hemispheric communication jointly influence the degree of syntactic lateralization.

White-matter microstructure of the splenium modulates right hemisphere ERP correlates of syntactic processing in older adults

“…Imaging and lesion studies consistently demonstrate the primary involvement of the left frontotemporal network for syntactic information processing in younger adults (Fedorenko et al, 2012;Griffiths et al, 2012;Zaccarella & Friederici, 2017), with cooccurring RH involvement reflecting more general semantic operations (Wright et al, 2012). ERP studies of syntactic processing report converging findings based on the divided VF paradigm and the P600 effect, a sustained posterior positivity beginning around 500 ms after ungrammatical stimuli onsets (Leckey & Federmeier, 2017;Yeh et al, 2020). In younger adults, the P600 effect is seen at the group level when grammatical errors are presented to the right visual field (RVF), which preferentially engages LH processing, but not when grammatical errors are presented to the left visual field (LVF), which prioritizes the RH.…”

“…Findings in younger adults support the compensatory role of the RH P600 to resolve uncertainty in syntactic information under greater task demands or when grammatical cues are impoverished, such as might be the case in older adult brains with reduced processing resources. For instance, RH P600 grammaticality effect is absent at the group level in young native speakers wherein syntactic processing is proficient and effective Yeh et al, 2020). However, RH P600 grammaticality effects were observed in a subset of intermediate-to-advanced second language learners with relatively low proficiency (Chen et al, 2018).…”