Abstracts

Rationale: Direct cortical electrical stimulation (DCS) during electrocorticographic (ECoG) recordings has been the gold standard for functional mapping during Phase II epilepsy surgery evaluations in adults. In children, the procedure duration may exceed their ability to cooperate. Recent studies have shown utility in mapping high-gamma frequency (70-150 Hz) cortical activity changes during functional tasks. We hypothesized that measuring changes in high-gamma ECoG during functional tasks would show results similar to DCS. Methods: Eleven patients, 6-20 years old, had subdural ECoG recorded during Phase II epilepsy surgery evaluation. Grid placements were based on Phase I presurgical evaluation, but in all patients this included coverage of the posterior frontal lobe, temporal lobe, and parietal lobe. Between 64 and 128 channels were recorded; grids were placed on the left hemisphere for 6 subjects and right for 5. ECoG was recorded simultaneously with Stellate amplifiers for clinical analysis and g.USBamp amplifiers (g.tec, Austria) sampled at 1200 Hz with no filtering applied. BCI2000 with the SIGFRIED system (Brunner et. al, 2009) was used at the bedside to analyze real-time changes in cortical activity in the 70-150 Hz power band. A resting baseline of 6 min. was compared to finger movement, tongue movement, lateral eye movements, passive stroking of the hand, listening to stories, music, and white noise, and picture naming, performed by the patients both overtly and covertly. Ten of the patients subsequently had conventional DCS with stimulation across pairs of adjacent electrodes to elicit motor movements and to inhibit picture naming to map language critical regions. Median nerve somatosensory evoked responses (MNSSEP) were done to map central sulcus. The electrodes showing activation with BCI were compared to DCS and MNSSEP findings. Results: Individual electrodes showed high-gamma changes during specific tasks, whereas DCS stimulation was between pairs of electrodes. MNSSEP showed phase reversal at pairs of electrodes, whereas hand sensation activation and motor activation were compared to arrive at central sulcus. Active tasks had specific instructions (finger movement, tongue movement, or lateral eye movement) and therefore elicited changes on a small subset of electrodes, compared to DCS which often elicited combined motor movements including primarily arm, hand, and face movement, and at times fingers, tongue, or visual gaze. Real-time mapping detected changes in cortical activity at common electrodes to DCS in 6/8 patients for hand motor, 5/6 patients for tongue/face, 2/2 patients for language production, 2/2 patients for lateral eye movements and 2/2 for central sulcus. Conclusions: Changes in high gamma power during functional tasks may be useful for pediatric patients particularly for localizing somatomotor regions. The current results for language concordance, though favorable, did not involve enough patients who also had language DCS for comparison.