Abstract Details

Seizure occurrence shows periodicity such as diurnal and circaseptan rhythms. However, the underlying biological basis for these rhythms is unknown. We utilized iEEG to capture HFOs (50-250 Hz) and identify periodic rhythms by sampling all implanted stereotactic electrodes, allowing a spatially extensive sampling of HFOs. We believe this work may lead to personalization of anti-seizure medication regimens.

We studied spontaneously occurring high-frequency oscillations (HFOs) in intracranial EEG (iEEG) for diurnal periodicity.

We included pediatric patients with drug-resistant epilepsy undergoing iEEG monitoring. iEEG was sampled at 2048 Hz and snipped into 5-minute iEEG segments every hour during a 24-hour period with patients off anti-seizure medications. We computed the number of HFOs in each iEEG channel within the 5-minute segment using the Montreal Neurological Institute detector in the RippleLab plug-in for MATLAB.  We looked for periodicity in the HFOs/channel/min (HFO density), using cosinor rhythmometry with a 24h period.

Ten pediatric patients (5 males, mean age = 12.75 years) were included with average number of electrodes/contacts = 126.3 +/- 27.7. Cosinor model found a midline estimating statistic of rhythm (MESOR) of 0.21 (95% CI 0.12, 0.29; p<0.001) and amplitude of 0.11 (95% CI 0.05, 0.16; p=0.008) for HFO density as a function of time of day. Both metrics achieved statistical significance against a null hypothesis of aperiodic pattern, although the acrophase was not significant 0.47 (95% CI -0.64, 0.59; p=0.405).    

We provide preliminary evidence for diurnal periodicity of HFOs in iEEG. There is a baseline HFO density (MESOR significantly different from null), which is significantly modulated by the time of day. However, our sample size may be too small to determine the true time of peak HFO density. Future studies will investigate differences in HFO density within and outside iEEG seizure-onset zone, and correlation with times of seizure occurrence.