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Bimodal coupling of ripples and slower oscillations during sleep in patients with focal epilepsy
Author(s) -
Song Inkyung,
Orosz Iren,
Chervoneva Inna,
Waldman Zachary J.,
Fried Itzhak,
Wu Chengyuan,
Sharan Ashwini,
Salamon Noriko,
Gorniak Richard,
Dewar Sandra,
Bragin Anatol,
Engel Jerome,
Sperling Michael R.,
Staba Richard,
Weiss Shennan A.
Publication year - 2017
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/epi.13912
Subject(s) - ripple , amplitude , epilepsy , temporal lobe , physics , coupling (piping) , electroencephalography , neuroscience , optics , psychology , materials science , quantum mechanics , voltage , metallurgy
Summary Objective Differentiating pathologic and physiologic high‐frequency oscillations ( HFO s) is challenging. In patients with focal epilepsy, HFO s 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 min intracranial electroencephalography ( 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 the 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 non‐SOZ (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 pathologic and physiologic events in patients with frontal and parietal SOZ .