Abstracts

Rationale: Mapping brain function is essential for tailoring epilepsy surgery. Stereo EEG (SEEG) has become more widely used compared to subdural electrodes for invasive EEG monitoring. Rapid real time high gamma frequency mapping (RTFM) has been developed for localizing brain function during invasive EEG monitoring with intracranial electrodes. We report findings of language and cognitive function mapping with RTFM in children and adolescents with medically intractable epilepsy who underwent invasive SEEG monitoring.


Methods: 47 patients (27 male / 20 female, mean age 13.5 +/- 4.6 years) who underwent RTFM during SEEG recording for medically intractable epilepsy were identified between December 2018 and June 2024, at Boston Children’s Hospital. 4 patients (Patients A,B,C,D) had atypical findings. 16 patients had electrode placement in temporal / inferior frontal regions, left side in 14 (including Patient C) and right side in 2 (Patients A, B), and underwent language mapping. Separately, Patient D had placement in the right parieto-occipital region and underwent visual function mapping. During SEEG, RTFM was performed using CortiQ system (gtec, Austria, approved for use in invasive EEG monitoring at Boston Children's Hospital). Custom-made stimulation paradigms were developed for each case, tailored to patients’ functional level and ability to cooperate for testing. Confirmatory functional testing was performed with cortical stimulation in all cases and compared with functional MRI (fMRI) when available.


Results: RTFM detected increased high gamma frequency activity (70-170 Hz) in regions activated by paradigm-related tasks. Functional mapping data was obtained without compromising data collection to capture seizures and localize onset. No seizure was triggered during RTFM. Patient A and B had bilateral language representation on fMRI, and language function was detected in the non-dominant right hemisphere; Patient A had expressive language activation in inferior frontal region; Patient B had receptive language activation in posterior superior temporal region, also face recognition and face memory in right anterior inferior temporal region. Patient C had receptive language activation posteriorly in the dominant left hemisphere parietal region. Patient D had visual function in right parietal region, anterior superior to primary vision region. In other cases, language was localized in expected regions in the dominant hemisphere (inferior frontal for expressive language, posterior temporal for receptive language). Results from cortical stimulation testing / fMRI were generally concordant with RTFM results. In 4 cases, areas outside of regular expected regions for function were activated with RTFM.


Conclusions: RTFM was able to localize language and cognitive function in children and adolescents undergoing SEEG for epilepsy surgery. With RTFM, at times expressive and receptive language function, face recognition and memory, widespread visual function were detected outside of regular expected regions. Capability to detect function in atypical locations is important when mapping in structurally and/or functionally abnormal brain, often with intractable epilepsy undergoing surgery.


Funding: N/A