Comparing Electrical Stimulation Functional Mapping with Subdural Electrodes and Stereo-EEG.

OBJECTIVES: Electrical stimulation mapping (ESM) is the clinical standard for functional localization with subdural electrodes (SDE). As stereo-EEG (SEEG) has emerged as an alternative option, we compared functional responses, after-discharges (ADs) and unwanted ESM-induced seizures (EIS) between the two electrode types.

METHODS: Incidence and current thresholds for functional responses (sensory, motor, speech/language), ADs and EIS were compared between SDE and SEEG using mixed models incorporating relevant covariates.

RESULTS: We identified 67 SEEG ESM and 106 SDE ESM patients (7207 and 4980 stimulated contacts respectively). We found similar incidence of language and motor responses between electrode types, however, more SEEG patients reported sensory responses. ADs and EIS occurred less commonly with SEEG than SDE. Current thresholds for language, face motor, upper extremity (UE) motor, and EIS significantly decreased with age. However, they were not affected by electrode type, premedication, or dominant hemispheric stimulation. AD thresholds were higher with SEEG than with SDE. For SEEG ESM, language thresholds remained below AD thresholds up to 26 years-of-age whereas this relationship was inverse for SDE. Also, face and UE motor thresholds fell below AD thresholds at earlier ages for SEEG than SDE. AD and EIS thresholds were not affected by premedication.

SIGNIFICANCE: SEEG and SDE have clinically relevant differences for functional brain mapping with electrical stimulation. While evaluation of language and motor regions is comparable between SEEG and SDE, SEEG offers higher likelihood of identifying sensory areas. A lower incidence of ADs and EIS, and a favorable relationship between functional and AD thresholds suggest superior safety and neurophysiologic validity for SEEG ESM than SDE ESM.