Abstract
Multilingual patients pose a unique challenge when planning epilepsy surgery near language cortex because the cortical representations of each language may be distinct. These distinctions may not be evident with routine electrocortical stimulation mapping (ESM). Electrocorticography (ECoG) has recently been used to detect task-related spectral perturbations associated with functional brain activation. We hypothesized that using broadband high gamma augmentation (HGA, 60–150 Hz) as an index of cortical activation, ECoG would complement ESM in discriminating the cortical representations of first (L1) and second (L2) languages. We studied four adult patients for whom English was a second language, in whom subdural electrodes (a total of 358) were implanted to guide epilepsy surgery. Patients underwent ECoG recordings and ESM while performing the same visual object naming task in L1 and L2. In three of four patients, ECoG found sites activated during naming in one language but not the other. These language-specific sites were not identified using ESM. In addition, ECoG HGA was observed at more sites during L2 versus L1 naming in two patients, suggesting that L2 processing required additional cortical resources compared to L1 processing in these individuals. Post-operative language deficits were identified in three patients (one in L2 only). These deficits were predicted by ECoG spectral mapping but not by ESM. These results suggest that pre-surgical mapping should include evaluation of all utilized languages to avoid post-operative functional deficits. Finally, this study suggests that ECoG spectral mapping may potentially complement the results of ESM of language.
Highlights
Multilingual speakers are individuals who communicate routinely in more than one language and outnumber monolingual individuals worldwide (French and Jacquet, 2004)
We report the results of ECoG spectral mapping and ESM of visual object naming in four patients for whom English is a second language
We hypothesized that ECoG spectral mapping of HGA would identify distinct as well as shared cortical regions involved in first (L1) and second (L2) language visual object naming
Summary
Multilingual speakers are individuals who communicate routinely in more than one language and outnumber monolingual individuals worldwide (French and Jacquet, 2004). Studies comparing cortical maps of first (L1) and second (L2) language processing using a variety of imaging methods have provided heterogeneous results. These maps are important for planning neurosurgical resections to preserve L1 and L2 function. Multilingual language organization has been studied in patients with permanent structural lesions resulting from tumors or strokes (Aglioti and Fabbro, 1993; Gomez-Tortosa et al, 1995; Aglioti et al, 1996), or temporary functional lesions produced during language mapping with electrocortical stimulation (Ojemann and Whitaker, 1978; Rapport et al, 1983; Bellotti et al, 1991; Graff-Radford et al, 1997; Roux and Tremoulet, 2002; Lubrano et al, 2004; Roux et al, 2004; Walker et al, 2004; Giussani et al, 2007; Kho et al, 2007; Serafini et al, 2008; Moritz-Gasser and Duffau, 2009), transcranial magnetic stimulation (TMS; Holtzheimer et al, 2005), electroconvulsive therapy (Chernigovskaya et al, 1983), and Wada testing (Berthier et al, 1990; Kho et al, 2007)
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