Abstract
Objective
Interictal spikes help localize seizure generators as part of surgical planning for drug-resistant epilepsy. However, there are often multiple spike populations whose frequencies change over time, influenced by brain state. Understanding state changes in spike rates will improve our ability to use spikes for surgical planning. Our goal was to determine the effect of sleep and seizures on interictal spikes, and to use sleep and seizure-related changes in spikes to localize the seizure onset zone.
Methods
We performed a retrospective analysis of intracranial EEG data from patients with focal epilepsy. We automatically detected interictal spikes and we classified different time periods as awake or asleep based on the ratio of alpha to delta power, with a secondary analysis using the recently published SleepSEEG algorithm. We analyzed spike rates surrounding sleep and seizures. We developed a model to localize the seizure onset zone using state-dependent spike rates.
Results
We analyzed data from 101 patients (54 women, age range 16-69). The normalized alpha-delta power ratio accurately classified wake from sleep periods (area under the curve = 0.90). Spikes were more frequent in sleep than wakefulness and in the postictal compared to the preictal state. Patients with temporal lobe epilepsy had a greater wake-to-sleep and pre-to-postictal spike rate increase compared to extra-temporal epilepsy. A machine-learning classifier incorporating state-dependent spike rates accurately identified the seizure onset zone (area under the curve = 0.83). Spike rates tended to be higher and better localize the seizure onset zone in NREM sleep than in wake or REM sleep.
Significance
The change in spike rates surrounding sleep and seizures differs between temporal and extratemporal lobe epilepsy. Spikes are more frequent and better localize the seizure onset zone in sleep, particularly in NREM sleep. Quantitative analysis of spikes may provide useful ancillary data to localize the seizure onset zone and improve surgical planning.
DIC