Patterns and predictors of atypical language representation in epilepsy

In the majority of the normal population, the left hemisphere is dominant for language. In epilepsy, a higher proportion of ‘atypical’ language representation is encountered. This can follow one of three patterns: (1) altered interhemispheric representation, where the spectrum of lateralisation is shifted to the right; (2) interhemispheric dissociation of linguistic subfunctions; or (3) intrahemispheric changes in representation. Knowledge of these patterns is essential for avoiding postoperative language deficits in epilepsy patients undergoing surgery. Several predictors of atypical language representation exist. It is more prevalent in left-handed individuals. Lesions in rough proximity to classical language areas are more associated with atypical language, although in some cases, remote lesions, such as in the hippocampus, can also lead to altered language representation. The more disruptive the lesion, the more likely atypical language is to be found. Widespread and frequent interictal epileptiform discharges are also associated with atypical language. Atypical language representation is more likely to be present when injury or epilepsy onset occurred at a young age. Thus, a subgroup of patients can be defined in whom atypical language representation is more likely to be found.