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Abstract
Background and Objectives Functional connectivity (FC) measures can be used to differentiate epileptogenic zones (EZs) from non-EZs in patients with medically refractory epilepsy. Little work has been done to evaluate the stability of stereo-EEG (SEEG) FC measures over time and their relationship with antiseizure medication (ASM) use, a critical confounder in epilepsy FC studies. We aimed to answer the following questions: Are SEEG FC measures stable over time? Are they influenced by ASMs? Are they affected by patient data collection state?
Methods In 32 patients with medically refractory focal epilepsy, we collected a single 2-minute prospective SEEG resting-state (awake, eyes closed) data set and consecutive 2-minute retrospective pseudo-rest (awake, eyes open) data sets for days 1–7 postimplantation. ASM dosages were recorded for days 1–7 postimplantation and drug load score (DLS) per day was calculated to standardize and compare across patients. FC was evaluated using directed and nondirected measures. Standard clinical interpretation of ictal SEEG was used to classify brain regions as EZs and non-EZs.
Results Over 7 days, presumed EZs consistently had higher FC than non-EZs when using between imaginary coherence (ImCoh) and partial directed coherence (PDC) inward strength, without accounting for DLS. These measures were demonstrated to be stable over a short-term period of 3 consecutive days with the same DLS. Between ImCoh FC differences between EZs and non-EZs were reduced with DLS decreases, whereas other measures were not affected by DLS. FC differences between EZs and non-EZs were seen during both resting-state and pseudo-rest conditions; ImCoh values were strongly correlated between the 2 conditions, whereas PDC values were not.
Discussion Inward and nondirected SEEG FC is higher in presumed EZs vs non-EZs and measures are stable over time. However, certain measures may be affected by ASM dose, as between ImCoh differences between EZs and non-EZs are less pronounced with lower doses, and other measures such as PDC are poorly correlated across recording conditions. These findings allow novel insight into how SEEG FC measures may aid surgical localization and how they are influenced by ASMs and other factors.
Glossary
- ASM=
- antiseizure medication;
- DLS=
- drug load score;
- EMR=
- electronic medical record;
- EMU=
- epilepsy monitoring unit;
- EZ=
- epileptogenic zone;
- FC=
- functional connectivity;
- FDR=
- false discovery rate;
- iEEG=
- intracranial EEG;
- ImCoh=
- imaginary coherence;
- IRB=
- institutional review board;
- LME=
- linear mixed effects;
- MEG=
- magnetoencephalography;
- PDC=
- partial directed coherence;
- RNS=
- responsive neurostimulation;
- SEEG=
- stereo-EEG;
- VUMC=
- Vanderbilt University Medical Center
Footnotes
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
↵* These authors contributed equally to this work as co–first authors.
- Received July 28, 2021.
- Accepted in final form February 1, 2022.
- © 2022 American Academy of Neurology
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