Passive Functional Mapping of Brain Language Area and Measuring Depth of Anesthesia Using Electrocoricography
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Every year, thousands of patients undergo craniotomy as an indispensable operation for their treatment procedure. These individuals are consisted, and not limited to those who suffer from brain lesions, tumors or intractable pharmaco-resistant epilepsy. Given the complicated anatomical structure of human brain and considering the fact that every single spot on the cortex is responsible to support vital sensory and cognitive functions, minimizing collateral damage to brain tissue located in the vicinity of the surgical region and consequently reducing post-surgical complications, is considered as an ultimate goal by neurosurgeons.Although many techniques have been developed and utilized to create pre-surgical passive brain mapping which provides patient-specific functional information, direct Electro-Cortical Stimulation (ECS) is considered the most standard technique. Although ECS is proved to be a useful practical method for functional mapping, yet applying it, not only requires a great deal of experience, but also is usually followed by some complications. Specially in the case of epileptic patients who need to be awakened during the surgery in order to perform a cognitive task, applying ECS could be very problematic, since it significantly increases the chance of seizure. In this study, we develop a novel method based on Electrocardiography (ECoG) in order to do passive functional mapping under anesthesia. This approach which has been successfully utilized on about 20 patients, includes recording ECoG signals while performing a simple auditory task. The fact that this paradigm does not require attentive participation of patients, makes it possible to be performed under anesthesia. Moreover, this procedure results in calculating a quantitative index for measuring depth of anesthesia which could potentially be used alongside with BiSpectral Index (BIS).