509 Electrocorticogram (ECoG) Gamma-band Modulations Induced by Cognitive-Linguistic Tasks for Intraoperative Functional Language Mapping During Awake Craniotomy

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INTRODUCTION: DCS is the gold standard of intraoperative functional language mapping but in predicting language functions and post-surgical outcomes. Moreover, DCS mapping can induce seizure with prolonged usage. METHODS: Eleven subjects underwent either temporal (eight) or frontal (three) lobe tumor resection surgeries involving awake language mapping using a 4x8 ECoG electrode grid (2.3mm contact exposure and 10mm pitch). A MATLAB/Simulink based real-time software system running on a portable laptop computer was used to map task-induced gamma-band modulations as 2D heat maps. Tasks included verbally responding to picture naming (object, action), written descriptive and auditory naming (AN). Auditory stimuli (> 1s) were provided during the auditory naming task, whereas visual stimuli (line drawings or written phrases) were presented during the other tasks. Bipolar DCS (2/4/6 mA, 60Hz, 2-4s) was applied at different electrode pairs while repeating the tasks. RESULTS: AN induced gamma-band (50-300Hz) modulations (ERS power> 2dB for >=200ms) on superior and middle temporal gyri (STG, MTG) and pars triangularis on the inferior frontal gyrus. Visual naming tasks modulated posterior MTG and inferior frontal gyrus. DCS-induced reproducible speech arrests occurred during different naming tasks while stimulating specific electrode pairs. DCS-responsive electrodes were not necessarily those with strong task-specific gamma-band activations. Five subjects developed postoperative speech deficits among which three (P7, P9, P11) remained with speech deficits after six months. In two (P9, P11) of those three subjects the resected cortical surface included gamma-band active regions but only one (P11) of those subjects had DCS positive regions resected. CONCLUSIONS: Intraoperative language mapping guided by gamma-band ECoG modulations induced by task-based activations in conjunction with DCS mapping can potentially be a better approach to preserve eloquent cortical language areas, thereby reducing post-operative language deficits.

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