Abstracts

Rationale: While the importance of ictal and preictal infraslow activity (ISA: ‹0.01 Hz) is well recognized in seizure localization, the role of postictal ISA remains unclear. Here, we investigated the postictal ISA changes in depth recordings. Methods: We studied 2 patients with temporal lobe epilepsy who had depth electrode implantation for presurgical workup. Clinical recordings were obtained with Nihon-Kohden system to define seizure onset based on conventional frequencies (1-70 Hz). We analyzed continuous ISA recordings acquired over 2-4 days using dedicated direct current (DC) amplifiers (Neuralynx Atlas, Bozeman, MT) in the true-DC (hardwired for DC) or hybrid-DC (no high pass filter) modes, both providing comparable measurements as there was no saturation. Postictal ISA changes were considered significant during the 60-minute window after seizure termination if they were ≥3 standard deviation compared to a baseline of average data 10 minutes immediately preceding the seizure. Seizures separated by < 60 min were not included in the analysis. Results: We analyzed 33 seizures over 2 days from patient A with bitemporal independent seizure onsets and failed prior right temporal lobectomy. Of 63 implanted contacts, he showed postictal ISA changes in 2 left hippocampal contacts contralateral to the conventional frequency seizure onset in the remnant right superior temporal gyrus. He underwent resection of the right superior temporal gyrus, but continued to have seizures postoperatively arising from the left temporal region on scalp recordings. We analyzed 18 seizures over 4 days from patient B with right temporal seizure onset and bitemporal independent interictal epileptiform discharges. Of 70 implanted contacts, she showed postictal ISA changes in 5 right temporal contacts concordant with the conventional frequency seizure onset. She underwent responsive neurostimulation. Postictal ISA changes were seen in all the seizures, ranged from 0.25 mV (in hybrid-DC) to 4 mV (in true-DC) depending on the type of recording, and persisted for 10-30 min postictally before showing a gradual recovery toward baseline. Conclusions: Our study suggests that the postictal ISA changes can be useful markers of seizure lateralization in temporal lobe epilepsy. It is possible that such prolonged postictal ISA changes reflect persistent redistribution of ions in the underlying astroglial network at the seizure focus in contrast to the relatively brief ictal ISA changes related to the transient discharge of the pyramidal neurons in the areas of seizure onset and propagation. Funding: None