Hemispheric lateralization and language skill coherence in temporal lobe epilepsy

Patients with an early onset of temporal lobe epilepsy (TLE) are at an increased risk for language reorganization. It is unknown whether this reorganization involves a full shift of all language skills to the contralateral hemisphere, or whether it can be partial and involve only a subset of language skills. In this study we report dominance concordance patterns for five separate language skills measured during the Intracarotid Amobarbital Procedure (IAP) for 124 TLE patients. We examined whether the language skills show similar or independent lateralization patterns. We compare these patterns in early versus late seizure onset groups with either a left or right temporal lobe seizure focus. The data showed that the rates of atypical representation ranged from 25.8% for reading to 14.5% of the sample for speech. A majority of patients (60%) showing atypical language representation do so on more than one skill. While multiple atypicalities were common, the proportion of patients showing atypical representation on all five skills was strikingly low (5.6% of the total sample). Our data suggest that language systems are not independent and do not shift and reorganize in isolation, and no pairs of skills seem more likely to reorganize than others. There was also evidence that language is not monolithic with all language skills reorganizing together. The latter suggests that the pressures compelling atypical representation may not work equally on all language skills.