Abstracts

Speech and language are established early in life, typically in the left hemisphere. Individuals who have suffered early injury to the brain from disorders such as epilepsy are known to have higher rates of atypical lateralization possibly through cognitive reorganization. An important unknown is the degree to which language functions reorganize en masse or whether shifts in laterality can occur independently for the separate language skills. The present study tested for potential independence among language functions by determining the laterality of five distinct language skills (auditory comprehension, speech, sentence repetition, visual confrontation naming, and single word reading) in a sample of temporal epilepsy patients. A total of 63 subjects (30 males, 33 females) underwent the IAP proceedure. Language ability on each of the skills was rated on a three-point scale (faultless, attempt with error, and failure). The resulting scores were utilized to classify performance on each skill as left dominant, right dominant, bilateral representation or failed performance. We only identified dominance or bilateral representation through the demonstration of competency. Analysis of variance on this laterality index score was conducted utilizing side of seizure focus and age of onset group as between-subject factors. Chi square analyses determined the association between laterality pattern and seizure focus/ age of onset group. A total of 38 patients (60% or 42 of 71) showed atypical language representation (bilateral representation or right hemispheric dominance) on at least one measure. Interestingly, both patients who showed atypical representation in all five language components together were left handed, indicating that left-handedness may be related to complete atypical dominance but not partial atypical dominance. When language reorganization occurs in an epilepsy population it is most likely to occur in 3 domains or more. Though not significant, the early left hemisphere lesion group showed a higher contribution to atypical lateralization from what could be thought of as [ldquo]truer[rdquo] atypicality (bilateral and right dominance) as opposed to the late right group which shows a higher contribution from the left hemisphere but some contribution from the right. The atypical representation shown may reflect reorganization, but congenital atypical lateralization is possible. This study met the aim of capturing even subtle contributions of the non-dominant hemisphere to language and was successful in assessing the patterns of atypical language dominance in an epilepsy population.