Hippocampal barques and their manifestation as 14&6 Hz positive spikes during sleep

Objective: This study investigates variations in hippocampal barque occurrence during sleep and compares findings to respective variations of their scalp manifestation as 14&6/sec positive spikes. Methods: From 11 epilepsy patients, 12 non-epileptogenic hippocampi with barques were identified for this study. Using the first seizure-free whole-night sleep stereo-encephalography (sEEG) recording, we performed sleep staging and measured the occurrence of barques and 14&6/sec positive spikes variants. Results: Hippocampal barques (total count: 9,183; mean count per record: 765.2 +/- 251.2) occurred predominantly during non-rapid eye movement (NREM) II sleep (total: 5,744; mean: 478.6 +/- 176.1; 62.2 +/- 6.0%) and slow-wave sleep (SWS) (total: 2,950; mean: 245.83 +/- 92.9; 32.0 +/- 6.2%), with rare to occasional occurrence in NREM I (total: 85; mean: 7.0 +/- 2.8; 0.9 +/- 0.4%), rapid eye movement (REM) (total: 153; mean: 12.75 +/- 4.0; 1.7 +/- 0.6) and wakefulness (total: 251; mean: 20.9 +/- 6.3; 2.9 +/- 0.9%). Barque rate increased during SWS (mean: 2.7 +/- 1.0 per min) compared to NREM II (2.2 +/- 1.0 per min) and other states (wakefulness: 0.1 +/- 0.0 per min; NREM I: 0.3 +/- 0.1 per min; REM: 0.1 +/- 0.0 per min). The 14&6/sec positive spikes variant (total count: 2,406; mean: 343.7 +/- 106.7) was present in NREM II (total: 2,059; mean: 249.1 +/- 100.2, 84.9 +/- 3.6%) and SWS (total: 347; mean: 49.5 +/- 12.8, 15.0 +/- 3.6%) stages, and absent from the rest of sleep and wakefulness. While all 14&6/sec positive spikes correlated with barques, only 44.7 +/- 6.1% of barques manifested as 14&6/sec positive spikes. Conclusions: Hippocampal barques are predominant in NREM II and SWS, and tend to increase their presence during SWS. Their scalp manifestation as 14&6/sec positive spikes is confounded by wakefulness, REM and NREM I stages, and "masked" by the co-occurrence of NREM II and SWS slow waves, and overlapping reactive micro-arousal elements. Significance: Our study highlighted the overnight profile of hippocampal barques, in relation to the respective profile of their scalp manifestation, the 14&6/sec positive spikes variant. CO 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.