Abstracts

Rationale: Functional human brain mapping is commonly performed during or prior to invasive brain surgery for the treatment of drug-refractory epilepsy or brain tumors. The current gold standard, electrocortical stimulation mapping (ESM), is time-consuming and often induces afterdischarges or seizures, and it may overestimate eloquent areas due to propagated effects of stimulation. Spectral analysis of electrocorticographic (ECoG) signals has recently emerged as a potential alternative to ESM. Many aspects of passive ECoG mapping are attractive in a clinical setting, especially the ability to rapidly evaluate brain function at all recording sites simultaneously. However, investigators have observed less correspondence between ECoG and ESM maps of language than between their maps of motor function. This may be due to the complexity of speech perception and production and the brain dynamics that support them.Methods: We evaluated seven patients who underwent invasive monitoring for seizure localization whose language and motor areas were identified using ESM. In addition to ESM, all patients performed language tasks including visual object naming and auditory word repetition during passive ECoG recordings. Because of the potential inaccuracies of ESM for functional localization, we decided to evaluate the accuracy of both ECoG and ESM with respect to cortical regions of interest (ROIs) drawn from the rich literature on fMRI during language tasks and the effects of brain lesions affecting speech production and perception.Results: The average sensitivity and specificity of ECoG relative to ESM were 69.9% and 83.5%, respectively, similar to previous studies of ECoG language mapping. Using the ROI approach we found that the sensitivity of ECoG was significantly greater than that of ESM (65.6% vs. 47.9%, respectively, p = 0.0068, McNemar’s test), while the specificity of ECoG was greater than that of ESM (86.2% vs. 78.0%, respectively), though not significantly so (p = 0.066, McNemar’s test).Conclusions: These findings suggest that both ESM and passive ECoG mapping offer approximations of the functional anatomy of individual patients, and that more studies are needed to compare their abilities to predict post-operative language outcomes.