Abstracts

Rationale: Electrocortical (ECS) mapping is a gold standard for functional brain mapping, though it takes a long time and has a risk of inducing after-discharges. Recently the passive functional activity mapping has been reported as a less invasive method instead of ECS mapping. One of the main target of functional mapping is language. However, we have not known an appropriate task to identify speech areas using passive functional activity mapping. Therefore, we performed several language tasks and compared functional detectability among tasks in passive functional mapping. Methods: We evaluated the data of high gamma activated mapping from three patients with dominant side temporal lobe epilepsy. We implanted subdural electrodes to cover the mesial temporal lobe, lateral temporal lobe and precentral dorsolateral frontal lobe in the subjective patients. For passive functional activity mapping by increasing the power of high gamma oscillation on each electrode, electrocorticography was recorded at a 1,200Hz sampling rate during language tasks using CortiQ (g.tec, Austria). Word naming and sentence reading tasks in aloud and silent were performed. Functional areas were detected according to increase the band power more than 30% at 60-170 Hz during each task compared to rest phase. In order to confirm the accuracy of passive functional activity mapping, we indicated ECS mapping by 6-12mA bipolar stimulation. Results: Tasks of word naming and sentence reading in aloud induced increase the band power in the primary sensory and motor language areas, but the primary motor area and surroundings were also activated. Word naming task in silent did not indicate sensory language areas. Sentence reading task in silent showed positive activation in the superior temporal gyrus and posterior temporal gyrus those was corresponding to the sensory language area. Sensory language areas that indicated by the passive functional activity mapping were matched as symptomatic areas in ECS mapping. It took an hour and a half on the average to perform passive functional activity mapping without complication. Conclusions: Passive functional mapping was a safe method to detect the appropriate functional areas. Task with several factors such as hearing and speech tended to show the wide cortical areas, because the power increase could also indicate the network. Simple and intermittent task was not enough to induce significant response of functional area. Since sentence reading task in silent was simple and continuous, it could induce significant band power in the proper areas which were correspond to the result of ECS mapping. Funding: None