Lateralization of language function in epilepsy patients: A high-density scalp-derived event-related potentials (ERP) study

Abstract

Language functional magnetic resonance imaging (fMRI) represents the clinical standard for language lateralization assessment in presurgical epilepsy evaluation, but still many patients experience postoperative language deficits. Event-related potentials (ERPs), especially the negative component around and after 400ms, are related to language processing and could therefore represent a complementary method of language lateralization assessment. Scalp EEG was recorded from 64 locations in 36 epilepsy patients and 37 controls during three visually presented language tasks: A short-term language memory task (differentiation memorized vs. unknown words), a phonological task (detection of rhymes in word pairs), and a semantic decision task (differentiation words vs. pseudowords). ERPs were analyzed in the 300ms-800ms epoch. Language fMRI was routinely obtained in patients. ERPs were significantly more negative over the left compared to the right hemisphere in all three tasks in patients and controls. Laterality indices showed highest concordance with fMRI for the Word/Pseudoword Task. ERPs of language processing were lateralized to the left hemisphere in the majority of epilepsy patients and controls. In patients, single-subject laterality indices showed high concordance with fMRI results. Results indicate that scalp-derived ERPs are a promising tool to investigate lateralization of language function in epilepsy patients.