High-resolution time course of hemispheric dominance revealed by low-resolution electromagnetic tomography

Objective: Auditory event-related brain potentials (ERPs) were recorded during a lexical decision task in response to linguistic and non-linguistic stimuli, to assess the detailed time course of language processing in general, and hemispheric dominance in particular. Methods: Young adults (n=17) were presented with pairs of auditory stimuli consisting of words, pseudowords and words played backwards in a lexical decision task. ERPs were recorded from 21 scalp electrodes. Current densities were calculated using low-resolution electromagnetic tomography (LORETA). Statistic non-parametric maps of activity were derived from the calculated current densities and the number of active brain voxels in the left and right hemispheres was compared throughout the processing of each stimulus. Results: Our results show that hemispheric dominance is highly time dependent, alternating between the right and left hemispheres at different times, and that the right hemisphere's role in language processing follows a different time course for first and second language. The time course of hemispheric dominance for non-linguistic stimuli was highly variable. Conclusions: The time course of hemispheric dominance is dynamic, alternating between left and right homologous regions, with different time courses for different stimulus classes.