Authors :
Presenting Author: Helen Brinyark, BS – The University of Alabama at Birmingham
Joshua LaRocque, MD, PhD – University of Pennsylvania; Soondos Kamel, N/A – Student, The University of Alabama at Birmingham; Erin Conrad, MD, MA – University of Pennsylvania; Rachel Smith, PhD – The University of Alabama at Birmingham
Rationale:
Resection or ablation of the seizure onset zone (SOZ) has proven to reduce or eliminate seizures that are not controlled with medication in patients with epilepsy. However, a range of 20-70% of patients undergoing this invasive surgery do not become seizure free and this may be because no biomarker of the SOZ exists. Intracranial EEG recorded during single-pulse electrical stimulation (SPES) can be analyzed to localize the SOZ. It has been shown that cortico-cortical spectral responses (CCSRs) that are evoked during SPES hold promise for SOZ localization.
Methods:
In this preliminary study, we analyzed CCSRs in ten epilepsy patients across four canonical frequency bands: theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz), low gamma (30-50 Hz). Intracranial EEG monitoring and SPES were performed on patients with drug-resistant epilepsy prior to surgical treatment. A short pulse was applied at 1 Hz to all adjacent pairs of electrode contacts, with 30 trials performed per pair. CCSRs were calculated using the MATLAB function cwt to perform a continuous Morse wavelet transform of each trial. The power spectrum for each contact pair was calculated by squaring the absolute value of the average wavelet transform result. A Gaussian CDF fit to the baseline distribution (450-150 ms before the stimulus) at each frequency was used to calculate p-values for each post-stimulus time-frequency power value at that frequency. P-values were corrected for multiple comparisons using the Benjamini-Hochberg procedure. For each contact pair, the number of significant power values occurring during the N1 peak time (10-50 ms after the stimulus) and during the N2 peak time (50-250 ms after the stimulus) intervals were totaled for each frequency band and normalized by the number of time-frequency points within the time-frequency zone.
Results:
We found that in nine out of ten patients, the most responsive (top 0.5%) channels contained clinician identified SOZ regions across different time-frequency zones (Figure 1). Our preliminary results suggest that contacts with significant spectral responses correlate with the SOZ. This finding corroborates the use of CCSRs as a candidate biomarker for the SOZ.
Conclusions:
In the future, we plan to further assess these responses by correcting for electrode locations and confirming SOZ contacts with post-surgical outcome data. In conclusion, this preliminary analysis suggests that CCSRs can be used to improve SOZ localization and increase success rates for those seeking surgical treatment for epilepsy.
Funding:
This work was funded by UAB Neuroengineering and a Blazer Fellowship.