Authors :
Presenting Author: Hart Fogel, BA – Columbia University Vagelos College of Physicians and Surgeons
Alexander Agopyan-Miu, MD – Department of Neurological Surgery – Columbia University Medical Center; Edward Merricks, PhD – Department of Neurology – Columbia University Medical Center; Andrew Michalak, MD – Department of Neurology – Columbia University Medical Center; Garrett Banks, MD – Department of Neurological Surgery – Baylor University Medical Center; Guy McKhann, MD – Department of Neurological Surgery – Columbia University Medical Center; Neil Feldstein, MD – Department of Neurological Surgery – Columbia University Medical Center; Sameer Sheth, MD/PhD – Department of Neurological Surgery – Baylor University Medical Center; Marla Hamberger, PhD – Department of Neurology – Columbia University Medical Center; Catherine Schevon, MD/PhD – Department of Neurology – Columbia University Medical Center
Rationale: Human and animal studies increasingly demonstrate that an anterior to posterior gradient along the hippocampus underlies distinct functional roles with unique extrahippocampal projections. As these connections may predict seizure spread, further characterization of temporal lobe epilepsy (TLE) syndromes with respect to the anterior-posterior hippocampal axis could enable more targeted surgical treatments. The objective of this study was to determine if seizure spread in TLE patients follows patterns of recruitment suggested by purported anterior and posterior temporal lobe subnetworks.
Methods: Thirty-five seizures from sixteen epilepsy surgery candidates with drug-resistant TLE were analyzed. Post-implant head CTs were coregistered to pre-implant volumetric brain MRIs to localize electrodes in Montreal Neurological Institute (MNI) space using iELVis. Seizure recruitment at a given site was defined using the previously developed and validated phase-locking value of high gamma signal (80-150 Hz) to low frequency ictal rhythms (2-50 Hz). A comparison of MNI-152 y-coordinates of recruited hippocampal recording sites based on recruitment status of sampled extrahippocampal structures was conducted using the Mann-Whitney U test corrected for multiple comparisons.
Results:
Patient characteristics were as follows: 10 right TLE, 6 left TLE, mean age 35.7 ± 10.2, 10 women, 6 men. Average y-coordinates of recruited hippocampus varied considerably across patients but were generally stereotypical for each patient (Figure 1). There was statistically significant variation in extrahippocampal recruitment in accordance with hippocampal recruitment localization on the MNI-152 y-axis (Table 1). Entorhinal cortex recruitment was associated with more anterior y-coordinates while amygdala, superior temporal gyrus, insula, lateral orbitofrontal cortex and medial orbitofrontal cortex recruitment were associated with more posterior y-coordinates.
Conclusions:
Seizures involving the hippocampus may be localized to different points along its anterior-posterior axis. This localization is associated with different patterns of extrahippocampal recruitment. This study provides proof of concept that TLE subtypes based on distinct anterior and posterior seizure recruitment networks can be identified. This finding is significant in that it may lead to more focused TLE surgical approaches for the purposes of diagnosis and treatment.
Funding: NIH R01 NS084142