Abstracts

Rationale: Our ability to understand and produce verbal language relies on the activation of specific functional regions of the brain. During invasive brain surgeries, such as those required for tumor resection or the treatment of epilepsy, it is critical to localize and preserve these regions to prevent post-surgical deficits in language function. Current methods to localize language activity, such as electrical cortical stimulation (ECS), have multiple limitations. ECS is time-consuming, potentially seizure provoking, and may not be technically feasible in pediatric populations due to immature myelination. Moreover, the interpretation of ECS is subjective, not standardized, and historically based on qualitative level 4 observational evidence. A rapid real-time passive method to map language areas using electrocorticographic (ECoG) signals as a surrogate of neuronal functional activation has the potential to supplement or replace current modalities and simplify clinical mapping procedurally, while maintaining the primary necessity of protecting eloquent cortex and improving post-surgical outcome. Methods: Several studies have described the use of passive functional mapping using ECoG signals in the broadband gamma band (70 ?" 110 Hz) to map expressive language function (Cervenka et al., 2013; Wang et al., 2016). To date, reports of ECoG-based mapping of receptive language function have been scarce (Korostenskaja et al., 2014). We here describe the first large-scale study that used ECoG for mapping receptive language areas. In this study, 23 patients listened to a part of the Boston Aphasia Battery while we recorded ECoG and identified receptive language areas in the temporal lobe using previously described methods (Brunner et al., 2009; Kapeller et al., 2015). Results: These methods were effective in producing a map of receptive language in 22 of the 23 patients. We then compared these maps with those derived using ECS mapping in those 11 of the 23 subjects for whom ECS data was available. Using a nearest-neighbor approach, sensitivity reached 95% while specificity reached 64%, indicating accurate identification of ECS+ electrodes. Conclusions: These results show that passive functional mapping reliably localizes receptive language areas, and that there is a substantial concordance between the ECoG- and ECS-based methods. They also point to a more refined understanding of the differences between ECoG- and ECS-based mapping, which may clarify the instances in which the two methods disagree. In summary, passive functional mapping provides a fast, robust, and reliable method for identifying receptive language areas without many of the risks and limitations associated with ECS. Funding: This work was supported by the NIH (EB00856, EB006356 and EB018783), the U.S. Army Research Office (W911NF-08-1-0216, W911NF-12-1-0109, W911NF-14-1-0440) and Fondazione Neurone.