Abstract
Neurosurgery on individuals with lesions around language areas becomes even more complicated when the patient is bilingual. It is thus important to understand the principles that predict the likelihood of convergent versus separate neuroanatomical organization of the first (L1) and the second language (L2) in these individuals. We reviewed all English-language publications on neurosurgical language mapping in bilinguals before January 2020 in three databases (e.g., PubMed). Our search yielded 28 studies with 207 participants. The reviewed data suggest several principles of language organization in bilingual neurosurgical patients: (1) separate cortical areas uniquely dedicated to each language in both anterior and posterior language sites are the rule rather than occasional findings, (2) In cases where there was a convergent neuroanatomical representation for L1 and L2, two factors explained the overlap: an early age of L2 acquisition and a small linguistic distance between L1 and L2 and (3) When L1 and L2 diverged neuroanatomically, more L1-specific sites were identified for early age of L2 acquisition, high L2 proficiency and a larger linguistic distance. This work provides initial evidence-based principles predicting the likelihood of converging versus separate neural representations of L1 and L2 in neurosurgical patients.
Highlights
Because over half of the world’s population communicates in two or more languages [1], understanding the principles underlying bilingual brain organization on a single-subject level is of importance to neurosurgery
Based on neuroimaging studies involving group analyses of healthy individuals, we know that the amount of neuroanatomical overlap between L1 and L2 can be modulated by a variety of factors, including the age of L2 acquisition [11,12], proficiency level of L2 [13], the amount of language exposure to L1 and L2 [14], the manner of L2 acquisition [15], the linguistic distance between L1 and L2 [16] and the modality of acquisition of L1 and L2 [17]
We solely focused on clinical language mapping studies that included data from bilingual neurosurgical patients
Summary
Because over half of the world’s population communicates in two or more languages [1], understanding the principles underlying bilingual brain organization on a single-subject level is of importance to neurosurgery. Based on neuroimaging studies involving group analyses of healthy individuals, we know that the amount of neuroanatomical overlap between L1 and L2 can be modulated by a variety of factors, including the age of L2 acquisition [11,12], proficiency level of L2 (and L1) [13], the amount of language exposure to L1 and L2 [14], the manner of L2 acquisition (formal/explicit versus informal/implicit) [15], the linguistic distance between L1 and L2 [16] and the modality of acquisition of L1 and L2 (oral versus signed) [17]. Most of these studies examined the factors in isolation
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