Bimodal coupling of ripples and slower oscillations during sleep in patients with focal epilepsy

Abstract

Summary Objective Differentiating pathological and physiological high-frequency oscillations (HFOs) is challenging. In patients with focal epilepsy, HFOs occur during the transitional periods between the up and down state of slow waves. The preferred phase angles of this form of phase-event amplitude coupling are bimodally distributed, and the ripples (80–150 Hz) that occur during the up-down transition more often occur in the seizure onset zone (SOZ). We investigated if bimodal ripple coupling was also evident for faster sleep oscillations, and could identify the SOZ. Methods Using an automated ripple detector, we identified ripple events in 40–60 minute intracranial EEG (iEEG) recordings from 23 patients with medically refractory mesial temporal lobe or neocortical epilepsy. The detector quantified epochs of sleep oscillations and computed instantaneous phase. We utilized a ripple phasor transform, ripple-triggered averaging, and circular statistics to investigate phase event-amplitude coupling. Results We found that at some individual recording sites, ripple event amplitude was coupled with sleep oscillatory phase and the preferred phase angles exhibited two distinct clusters (p<0.05). The distribution of the pooled mean preferred phase angle, defined by combining the means from each cluster at each individual recording site, also exhibited two distinct clusters (p<0.05). Based on the range of preferred phase angles defined by these two clusters, we partitioned each ripple event at each recording site into two groups: depth iEEG peak-trough and trough-peak. The mean ripple rates of the two groups in the SOZ and NSOZ were compared. We found that in the frontal (spindle, p=0.009; theta, p=0.006, slow, p=0.004) and parietal lobe (theta, p=0.007, delta, p=0.002, slow, p=0.001) the SOZ incidence rate for the ripples occurring during the trough-peak transition was significantly increased. Significance Phase-event amplitude coupling between ripples and sleep oscillations may be useful to distinguish pathological and physiological events in patients with frontal and parietal SOZ.

Phase‐amplitude coupling between interictal high‐frequency activity and slow waves in epilepsy surgery

“…Our study was not designed to determine whether MI (>150 Hz & 3‐4 Hz) is more useful than other interictal HFA measures. Some investigators have suggested that characterization of the angle of slow‐wave phase preferentially coupled with HFA was useful in localization of SOZ . For measurement of the amplitude of HFA, the present study employed a high‐pass filter of 150 Hz; thus, the amplitude of HFA 80‐150 Hz may have only modestly contributed to computation of MI (>150 Hz & 3‐4 Hz) .…”

Interictal coupling of HFOs and slow oscillations predicts the seizure‐onset pattern in mesiotemporal lobe epilepsy

“…17 HFOs, divided into ripples and FRs, were detected automatically using the MNI detector 19 (The detector is also implemented in RIPPLELAB 20 ). 17 HFOs, divided into ripples and FRs, were detected automatically using the MNI detector 19 (The detector is also implemented in RIPPLELAB 20 ).…”

“…Ripples usually predominate during LVF, whereas fast ripples (FRs) are more frequent during PS seizures. 17 In our previous study, we demonstrated that in the interictal period, higher values of PAC exist in the SOZ compared to normal channels 13 ; however, how different types of epilepsy or seizures are associated with different coupling patterns has not been investigated yet. 7 Phase-amplitude coupling (the coupling between the amplitude of high-frequency activity and the phase of the lowfrequency band; PAC) has been the subject of many studies, not only in normal brain activity, but also in patients with epilepsy.…”

Strong coupling between slow oscillations and wide fast ripples in children with epileptic spasms: Investigation of modulation index and occurrence rate

“…37 Further studies considering preferred phase angles of coupling may explain the electrophysiological features and the detailed epileptic network activity of ES. 37 Further studies considering preferred phase angles of coupling may explain the electrophysiological features and the detailed epileptic network activity of ES.…”