Language after hemispherectomy in childhood: contributions from memory and intelligence

After hemispherectomy (removal or disconnection of an entire cerebral hemisphere) in childhood for treatment of intractable epilepsy, gross speech and language functions are often rescued. Whether more complex functions, such as syntactic processing, are selectively impaired, remains controversial. Here we present a cross-sectional study of expressive and receptive language functions in 30 patients who have undergone hemispherectomy (17 left, 13 right). The patients had developed epilepsy-induced pathology either during the pre/perinatal period (19 cases), or after a period of normal development (11 cases; onset range=20 months to 10 years). The patients were assessed at least 1 year post surgery on tests of receptive vocabulary, expressive and receptive grammar, instruction comprehension, and semantic association. Measures of verbal and nonverbal intelligence, short-term verbal memory, and working memory were also obtained. Principal component analysis revealed that two core components could be extracted from the five language measures, one reflecting receptive vocabulary abilities, and the other a composite of the other four measures. Regression analyses revealed that the best predictor of the composite language score was the short-term verbal memory score with some contribution from verbal intelligence, while the only predictor of receptive vocabulary was verbal intelligence. The results suggest that during childhood the lone left and right hemispheres have a similar potential for developing an adequate level of receptive vocabulary. However, congenital pathology affecting either hemisphere, and postnatal damage to the left hemisphere result in substantial language deficits that are reflected also in limitations in short-term verbal memory, and, to a lesser extent, in verbal intelligence.