Anti-seizure Medications Alter the Brain Connectivity as Measured by Intracranial Cortico-cortical Evoked Potentials
Abstract number :
3.037
Submission category :
1. Basic Mechanisms / 1C. Electrophysiology/High frequency oscillations
Year :
2024
Submission ID :
222
Source :
www.aesnet.org
Presentation date :
12/9/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Serdar Akkol, MD, PhD – University of Alabama at Birmingham
Helen Brinyark, BS – University of Alabama at Birmingham
Aparna Vaddiparti, MD – University of Alabama at Birmingham
Rachel Smith, PhD – University of Alabama at Birmingham
Benjamin Cox, MD – University of Alabama at Birmingham
Rationale: Anti-seizure medications (ASMs) affect epileptic seizures through distinct neuronal mechanisms. They can also lead to multiple cognitive and behavioral side effects. Some of the beneficial and adverse effects can be explained by the modulation of brain connectivity. Cortico-cortical evoked potentials (CCEPs) are voltage deflections recorded during single pulse electrical stimulation (SPES) and can measure the effective connectivity with high temporal and spatial resolution. CCEPs can help us investigate the interactions between brain regions and how ASMs change these interactions. However, the effect of ASMs on CCEPs is unknown. We hypothesized that ASMs alter the connectivity within seizure network more than other brain areas.
Methods: Two patients underwent epilepsy monitoring with depth electrodes for medically refractory epilepsy. On the day following the electrode implantation, patients underwent SPES producing CCEP while on ASMs (ASM-ON). Due to patients not having any typical seizures, a second SPES session was performed while off ASMs (ASM-OFF). We recorded a total of 156 and 177 bipolar channels in these two patients, respectively. We stimulated a total of 5 seizure onset zones (SOZ), 32 irritative zones (IZ), 2 early propagation zones (EPZ) and 40 non-involved zone (NIZ) pairs. All channels were labeled by the clinical team based on recorded seizures. SPES was applied with 5mA, 150µsec square wave pulses at 1 Hz frequency. We calculated latencies and amplitudes of the N1 and N2 peaks on individual CCEP responses and statistically compared the values with a t-test. We averaged the CCEPs at each recorded channel and calculated the root-mean-square (RMS) as a well-accepted measure of effective connectivity.
Results: We found that CCEPs change differently based on the type of stimulated electrodes (Figure 1). Specifically, latencies were longer, and amplitudes were lower for N1 and N2 while on ASMs compared to off. N1 and N2 responses to SOZ or EPZ stimulation were affected more frequently than to IZ or NIZ. Regarding effective connectivity, we found that there was decreased effective connectivity towards the IZ in response to the stimulation of SOZ, IZ and NIZ channels while on ASMs (Figure 2).
Conclusions: The changes in the CCEP responses when on ASMs was hypothesized to reflect the changes in brain connectivity. Overall, we found that ASMs affected the seizure network more than the healthy network. CCEPs had longer latencies with lower amplitude when the patients were on ASMs compared to off ASMs. The shortened CCEP latency on ASMs might be the result of activation of fewer white matter pathways and slower neuronal activity. This study is the first study revealing with high spatiotemporal resolution that ASMs can alter brain connectivity more for seizure network than outside the seizure network.
Funding: AES Junior Investigator Awards to Dr. Benjamin Cox and Dr. Rachel June Smith
Basic Mechanisms