The left hemispheric lateralization for language: a High-Density EEG protocol validation study

Background: Left hemisphere is known to be dominant for language in general population, however, there are heterogeneous results in literature, possibly attributable to the experimental task used. The present protocol validation study aimed to identify the most suitable task to investigate the process of language lateralization by visualizing the dynamics of EEG components and mapping the corresponding brain regions. Methods: We collected data of n=30 participants, all adult, healthy, right-handed, and Italian native speakers (15F/15M, mean age=23 ± 2.3). Participants executed two computerized linguistic tasks (Rhyme Judgment and Verb Generation), while the EEG activity was recorded with a 256-channels High-Density EEG. Spatial localization of electrodes was performed using 3D scanning. After preprocessing steps, we created the head model for every subject using their own structural magnetic resonance images, then we performed analyses of ERP components and neural generators at group level. For behavioral data, we analyzed mean accuracy and reaction time. Results: Source analysis showed that Rhyme Judgment task determined greater left hemisphere lateralization for both early (150, 375, 625 ms) and late (CNV) ERPs, while Verb Generation task showed a more distributed activation pattern involving right hemisphere. Performances in both tasks were optimal (>95% of accuracy, <1000 ms of reaction time). Take home message: Rhyme Judgment task is a valuable approach to identify left hemispheric lateralization for language.