Rationale: Mapping brain function is essential when tailoring surgery for pediatric epilepsy. Stereo EEG (SEEG) has become more widely used compared to subdural electrodes for invasive EEG monitoring. We report rapid real time high gamma frequency mapping (RTFM) for localizing motor and sensory function in children and adolescents with medically intractable epilepsy who underwent invasive EEG monitoring with SEEG recordings.
Methods:A total of 43 patients (24 male and 19 female, mean age 12.2 +/- 4.3 years) who underwent SEEG recording for medically intractable epilepsy were identified between December 2018 and April 2023, at Boston Children’s Hospital. A total of 32 of these patients (17 male and 15 female, mean age 13.0 +/- 4.4 years) had electrode placement in the perirolandic region (left side in 14 cases, right side in 18 cases) and underwent functional mapping of motor and sensory function.
During the SEEG study, RTFM was performed using the CortiQ system (gtec, Austria). The CortiQ system was approved for use in invasive EEG monitoring cases at Boston Children's Hospital. Custom-made stimulation paradigms were developed for each case, tailored to the patients’ functional levels and abilities to cooperate for testing. Confirmatory testing for function was performed with cortical stimulation in all cases.
Results: RTFM detected increased high gamma frequency activity (70-170 Hz) in regions activated by paradigm-related tasks. The CortiQ system was able to obtain functional mapping data without compromising SEEG data collection to capture seizures and localize onset. No seizures were triggered during RTFM testing.
Motor function was localized in precentral regions in 28 cases, and sensory function was localized in postcentral regions in 20 cases (localization of both motor and sensory function occurred in 16 cases). Motor function was localized for face in 17, hand in 20 and leg in 6 cases; sensory function was localized for face in 6, hand in 17, and leg in 1 case, respectively.
Results from confirmatory testing with cortical stimulation testing were generally concordant with results from RTFM. Broader areas may occasionally be activated with RTFM, depending on the paradigm used.
Activation of both motor and sensory areas were seen with paradigms involving motor function, when SEEG electrodes were implanted in relevant regions (often with hand function).
Conclusions: RTFM with 70-170 Hz with multiple depth electrodes in SEEG recordings appears able to localize motor and sensory function in children and adolescents undergoing invasive EEG monitoring for epilepsy surgery.
RTFM was able to provide functional data confirmed with multiple paradigms. RTFM appeared helpful and complimentary in functional mapping, in particular when evaluating regions with low seizure threshold where cortical simulation is limited for safety, or areas of high threshold for stimulating function.
RTFM may detect broader but important functional networks, beyond cortical stimulation. Additional studies will be necessary to further optimize the use of this technology and evaluate its ability to decrease the risk of functional morbidity.
Funding: No funding was received in support of this abstract.