Authors :
Presenting Author: Vasanth Raja, BS – Touro University California College of Osteopathic Medicine
Jordan Seliger, BA – Stanford Neuroscience Clinical Research Group
Adam Fogarty, BS – Stanford Comprehensive Epilepsy Center
Kimford Meador, MD – Stanford Comprehensive Epilepsy Center
Scheherazade Le, MD – Stanford Comprehensive Epilepsy Center
Babak Razavi, MD – Stanford Comprehensive Epilepsy Center
Rationale:
Pre-surgical evaluation is vital for assessing potential risk of post-operative memory deficits in patients with drug-resistant temporal lobe epilepsy. The Wada test is one such test that is used for determining language dominance and risk of post-operative memory deficits. By anesthetizing portions of the brain, the test simulates resection while the patient performs language and memory tasks. In some cases, the Wada test is performed on patients implanted with intracranial EEG (iEEG). This study assessed changes in quantitative iEEG in response to anesthesia, which may serve as a potential biomarker for localizing the seizure-onset zone (SOZ).
Methods:
Retrospective data from eight patients who underwent Wada testing with iEEG as part of their routine pre-surgical evaluation were included in these analyses. Grid, strip, and/or depth electrodes were implanted across several brain regions including the mesial temporal lobe (i.e., amygdala, hippocampus). iEEG data were sampled at 500 Hz. Power spectral density was computed across frequency bands ranging from 0.5-250 Hz, for each iEEG channel in a bipolar montage across time using 2-second, non-overlapping, sliding windows starting two minutes prior to anesthetic injection and up to 14 minutes post-injection. SOZ was based on visual review of the iEEG by fellow and board-certified attending epileptologists. The current analyses examined dynamics in pre-injection baseline power, post-injection peak power relative to pre-injection baseline, and time to reach peak power.
Results:
Overall, iEEG power increased post-injection across different frequency bands and brain regions followed by gradual decrease towards pre-injection baseline. The change in power over time relative to pre-injection baseline was significantly different between SOZs and non-SOZs across all frequency bands for subjects with depth electrodes (ps < 0.05).