Abstracts

Rationale: Stereo EEG (SEEG) has become more widely used for invasive EEG monitoring for epilepsy surgery, and mapping important brain function is essential for tailoring the surgery. 

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 RTFM for receptive language function mapping in children and adolescents with medically intractable epilepsy who underwent invasive SEEG monitoring, demonstrating the benefits of RTFM.

Methods: 50 patients (29 male / 21 female, mean age 13.6 +/- 4.8 years) who underwent SEEG recording for medically intractable epilepsy were identified between December 2018 and December 2024, at Boston Children’s Hospital.

11 patients had electrode placement in the superior temporal regions, and underwent mapping for receptive language function. During SEEG, RTFM was performed using the 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: 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 seizures were triggered during RTFM.

Responses to auditory stimuli were detected in all 11 cases. In 7 of them, receptive language was localized with RTFM using a combination of paradigms, comparing paradigms of auditory stimuli with and without language. RTFM was well tolerated, while allowing to use a combination of multiple paradigms with longer durations compared to standard cortical stimulation. Paradigms were also adjusted to the developmental and cognitive level at the bedside. RTFM was recording simultaneously from all implanted electrodes, and able to detect responses, even in locations outside of expected anatomical regions.

Conclusions: In structurally and/or functionally abnormal brain undergoing epilepsy surgery, localization of language function is often altered, and obtaining as much information is essential for surgical planning. In children and adolescents undergoing SEEG for epilepsy surgery, RTFM was able to identify areas of receptive function with a combination of paradigms, comparing paradigms of auditory stimuli with and without language. RTFM has much tolerability and flexibility for using multiple combinations, also allowing adjustments of paradigms at the bedside. This is a great advantage for increasing information and improving localization of receptive language function, even in challenging pediatric cases with limited cooperation.

Funding: None