Abstract
Stereo-electroencephalography (sEEG) is a method that uses stereotactically implanted depth electrodes for extra-operative mapping of epileptogenic and functional networks. sEEG derived functional mapping is achieved using electrical cortical stimulations (ECS) that are currently the gold standard for delineating eloquent cortex. As this stands true especially for primary cortices (e.g., visual, sensitive, motor, etc.), ECS applied to higher order brain areas determine more subtle behavioral responses. While anterior and posterior language areas in the dorsal language stream seem to share characteristics with primary cortices, basal temporal language area (BTLA) in the ventral temporal cortex (VTC) behaves as a highly associative cortex. After a short introduction and considerations about methodological aspects of ECS using sEEG, we review the sEEG language mapping literature in this perspective. We first establish the validity of this technique to map indispensable language cortices in the dorsal language stream. Second, we highlight the contrast between the growing empirical ECS experience and the lack of understanding regarding the fundamental mechanisms underlying ECS behavioral effects, especially concerning the dispensable language cortex in the VTC. Evidences for considering network architecture as determinant for ECS behavioral response complexities are discussed. Further, we address the importance of designing new research in network organization of language as this could enhance ECS ability to map interindividual variability, pathology driven reorganization, and ultimately identify network resilience markers in order to better predict post-operative language deficit. Finally, based on a whole body of available studies, we believe there is strong evidence to consider sEEG as a valid, safe and reliable method for defining eloquent language cortices although there have been no proper comparisons between surgical resections with or without extra-operative or intra-operative language mapping.
Highlights
Cognitive mapping of the cerebral cortex using electrical cortical stimulation (ESC) is a safe, readily available technique that has largely contributed to current practice in functional neurosurgery
All resected basal temporal language area (BTLA) positive sites were located within the 30 mm from the temporal tip and were included within the usual limits of the so-called standard left anterior temporal lobectomy. These results strongly suggest that resection of BTLA increases the risk of post resection early naming decline and plead for an important structural role of this area
Functional language mapping using Electrical Cortical Stimulations (ECS) has a long history mainly supported by empirical clinical knowledge
Summary
Cognitive mapping of the cerebral cortex using electrical cortical stimulation (ESC) is a safe, readily available technique that has largely contributed to current practice in functional neurosurgery. It has remained one of the most complex endeavor for functional neurosurgery, especially epilepsy surgery. In indispensable language eloquent cortices discussed, we will mainly address the issue of reliability of ECS for mapping brain areas considering individual variability or pathology driven reorganization. In the last section, focusing on the dispensable language eloquent cortices in the ventro-temporal cortex, we will mainly address the pertinence of ECS for mapping language considered as a complex function within distributed dynamic systems organized in spatially segregated modules
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