Organization of language areas in bilingual patients: a cortical stimulation study

In an attempt to gain a better understanding of how multiple languages are represented in the human brain, the authors studied bilingual patients who underwent surgery for brain tumors, during which the authors mapped cortical language sites by using electrostimulation.

Reading, counting, and word retrieval tasks were studied in 12 right-handed bilingual patients with no language deficit. All bilingual patients were native to France. One patient spoke four languages. The patients constituted a nonhomogeneous group in terms of language proficiency or age of acquisition. Languages were evaluated and classified into three major groups, depending on proficiency and date of acquisition. Strict conditions of language site validation were applied, separating typical anomia sites from speech arrest or other language sites (such as hesitation sites). A total of 30 speech arrest sites, 16 anomia sites, and three sites of language difficulties (not typically classified as speech arrest) were found throughout the 26 language studies performed. Strict overlapping of language areas (for all language tasks) was found in five patients, whereas the remaining seven had at least one area that was language-specific and sometimes task-specific. Specific areas for a particular language were found for word retrieval tasks (anomia) in eight sites (50%) but also in six (20%) of the reading or counting sites (speech arrest), either in frontal (three patients) or in temporoparietal (four patients) regions. Among the four early bilingual patients tested (languages acquired before the age of 7 years), three had language-specific cortical areas. Interestingly, six patients in this series who had a discrepancy between two languages did not have more cortical areas devoted to the less proficient language (with acknowledgment of the limit in cortical exposure available for testing by the craniotomy).

In this series, the authors found that bilingual patients could have common but also different cortical areas for both languages in temporoparietal areas and in frontal areas. In some cases, the authors found that language tasks such as counting, reading, or word retrieval in different languages can be sustained by language- and task-specific cortical areas. In bilingual patients, cortical mapping should ideally be performed using different language tasks in all languages in which the patient is fluent.