Abstracts

Rationale: Functional mapping of eloquent cortex is typically performed prior to resective brain surgery to minimize post-surgical morbidity. Electrical cortical stimulation (ECS) and functional magnetic resonance imaging (fMRI) are the major two clinical techniques to perform this mapping. ECS is based on a lesional effect and provides two-dimensional maps, while fMRI is based on a metabolic effect and provides three-dimensional maps of eloquent cortex. While ECS and fMRI are widely accepted to provide clinical value, they have some or all of the following three major limitations: (1) they depend on experts and/or post-hoc analysis; (2) they are based on an indirect measure; (3) they produce results in anatomical space (fMRI) or electrode space (ECS), but not both at the same time. We had previously described (Brunner et al., 2009) the development and validation of a new functional mapping technique (SIGFRIED) that uses task-related electrocorticographic (ECoG) signals in the gamma (i.e., 70-110 Hz) band to provide a map of eloquent cortex in real time. In the present study, we are extending the capacities of this method to three-dimensional mapping. Methods: We evaluated the clinical feasibility of this procedure in a study with 5 human epilepsy patients that underwent surgical implantation of 64-128 subdural electrocorticographic electrodes. For each patient, we co-registered the cortical anatomy defined by a pre-operative MRI with the electrode locations defined by a post-operative CT, which resulted in a three-dimensional surface cortical model and the locations of the electrodes. We then visualized the output of our SIGFRIED technique during language- and motor-tasks directly on the three-dimensional cortical model in real time. Specifically, the patients were asked to perform an average of five 10-sec trials of cued motor (e.g., manipulating a rubik's cube) and receptive language tasks (e.g., listening to voices and tones). While the subjects performed these tasks, our SIGFRIED procedure provided two- and three-dimensional maps of cortical areas whose ECoG activity changed with the task. We then validated our results against the results derived using ECS. Results: Validation showed high concordance with ECS, it also revealed two shortcomings of our procedure: (1) task-relevant eloquent cortex may not be essential to function, e.g., in the case of bi-lateral language function; (2) ictal activity may obscure task-relevant changes. Conclusions: Despite the discussed shortcomings, the extension of our established SIGFRIED technique to three-dimensional real-time mapping further increases the potential value of this new mapping technique in invasive surgery protocols.