Language Mapping in Multilingual Patients: Electrocorticography and Cortical Stimulation During Naming

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.

Ictal propagation of high frequency activity is recapitulated in interictal recordings: Effective connectivity of epileptogenic networks recorded with intracranial EEG

“…We computed the time-frequency energy distribution of ictal activity in all recorded channels using a matching pursuit (MP) algorithm (Mallat and Zhang, 1993), which has been previously successfully used for detection of epileptic activity (Jouny et al, 2007a; Jouny et al, 2003), as well as functional activity (Boatman-Reich et al, 2010; Cervenka et al, 2011a; Cervenka et al, 2013a; Cervenka et al, 2013b; Cervenka et al, 2011b). MP is an iterative procedure that decomposes signal x(t) into a linear combination of members of a specified set of functions.…”

Spatial-temporal functional mapping of language at the bedside with electrocorticography

“…29,30 It has long been recognized that cortical stimulation can affect function at a distance, 7 and that ESM does not always predict postoperative language outcomes. 10,26,31 This concern is perhaps best illustrated in somatosensory and motor cortices, where the effects of lesions are more predictable. Although stimulation of postcentral gyrus often elicits motor responses, resection of this gyrus causes sensory impairments and apraxia, but not weakness per se.…”

“…Although some studies have indicated poor sensitivity and specificity of ECoG mapping in relation to ESM (e.g., specificity of 78% and sensitivity of 38% during visual object naming 12 ), recent reports have suggested that in some instances it can be more predictive of postoperative language impairments than ESM. 10,26,27 More work will be required to correlate surgical outcomes with the location of resected and preserved sites identified by ESM and STFM.…”

Proceedings of the Third International Workshop on Advances in Electrocorticography

“…To date, studies of the clinical utility of ECoG for preoperative functional mapping have been promising [82], but clinical decisions about surgical resections continue to rely on ESM. More studies are needed to assess the relative abilities of ECoG and ESM to predict postresection neurological impairments.…”