Varying Stimulation Intensity for Cortico-cortical Evoked Potentials Improves Seizure Localization
Abstract number :
2.046
Submission category :
3. Neurophysiology / 3E. Brain Stimulation
Year :
2022
Submission ID :
2204164
Source :
www.aesnet.org
Presentation date :
12/4/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:23 AM
Authors :
Mark Hays, – Johns Hopkins University; Rachel Smith, PhD – Johns Hopkins University; Yujing Wang, PhD – Johns Hopkins University; Christopher Coogan, MS – Johns Hopkins University; Sridevi Sarma, PhD – Johns Hopkins University; Nathan Crone, MD – Johns Hopkins University; Joon Kang, MD – Johns Hopkins University
Rationale: Successful surgical treatment for patients with medically refractory epilepsy (MRE) relies on accurate localization of the seizure onset zone (SOZ). Single pulse electrical stimulation (SPES) is an active technique that may supplement passive intracranial EEG (iEEG) monitoring to help identify this region by probing seizure networks and quantifying effective connectivity through evoked responses. However, since stimulation parameters such as current intensity also influence these responses, it is necessary to understand how parameter choice will affect the ability to delineate epileptogenic networks. Therefore, we sought to determine how these responses, known as cortico-cortical evoked potentials (CCEPs), for sites inside and outside the SOZ differed over a range of current intensities and whether those differences could improve SOZ localization.
Methods: SPES was conducted in 15 patients with MRE undergoing iEEG monitoring using incremental titrations of current intensity followed by full blocks at a maximal intensity. At each intensity, observed CCEPs were quantified by the N1 amplitude and were classified as being within the SOZ or non-seizure onset zone (nSOZ) based on response site location. The effect of current intensity on the amplitude and spatial distribution of CCEPS was compared between the SOZ and nSOZ groups. We then used logistic regression models to classify connections and sites in the SOZ or nSOZ using the N1 amplitudes in response to the ranges of current intensities used. Performance was compared between models using responses to titrations, responses to only the single maximal intensity, or all responses.
Results: We found that at 2 mA and above, SOZ responses showed increasingly greater N1 amplitude compared to nSOZ responses, especially when the stimulation site was also within the SOZ. The distribution of SOZ responses was maximized by 4 to 6 mA while that of nSOZ steadily increased. Logistic regression models that incorporated responses to the titrations achieved better separability of SOZ and nSOZ compared to models relying on responses to only one maximal intensity for connection-based (median area under the curve [AUC] across patients of 0.75 vs. 0.64) and site-based (median AUC of 0.86 vs. 0.77) classification.
Conclusions: We demonstrated how the amplitude and distribution of CCEPs in SOZ and nSOZ sites differ over a range of stimulating current intensities and that responses to varied current intensities can improve discriminability of SOZ and nSOZ regions compared to responses to only one maximum intensity. This study provides insight into the underlying excitability of epileptogenic regions and how differences in current-dependent amplitudes of CCEPs may be used to better localize epileptogenic sites.
Funding: This work was supported by the NIH NINDS Grant R01 NS115929.
Neurophysiology