Interictal ripples nested in epileptiform discharge help to identify the epileptogenic zone in neocortical epilepsy

Progress and remaining challenges in the application of high frequency oscillations as biomarkers of epileptic brain

“…Regional differences in the behavior and nature of HFOs have also been reported in human studies, particularly in mesial temporal, motor and occipital structures [15,45,51,55,56,59,65]. …”

“…This is supported by studies using different approaches in defining the pHFOs and nHFOs, e.g. considering task-induced HFOs as nHFOs [15,55], or HFOs associated with interictal epileptiform discharges (IEDs) as pHFOs [21,56]. Also, resection of the high-rate HFOs regions was found to be correlated with favorable surgery outcome [45,49,50,52,57,58].…”

“…It was shown that removal of the HFOs occurring on a flat, non-oscillatory background was correlated with better surgery outcomes, while there was no such relation with the resection of the HFOs occurring in an oscillatory background [62]. The channels showing continuous high frequency activity showed no association with SOZ or epileptic lesion, they were instead found to be predominant in the mesial temporal and occipital regions [56,63]. Thus these continuous oscillatory activities were suggested as physiologic patterns specific to certain brain regions.…”

“…The association between pHFOs and interictal epileptiform discharges (IEDs) was investigated by various studies [21,22,46,56]. Wang et al, [21] classified neocortical ripples into two subtypes: type I ripples superimposed on an IED, and type II ripples independent of any epileptiform discharges.…”

“…These authors later reported a significant correlation between the surgery success and the higher resection ratio of the fast ripples and the type I ripples but not type II ripples. [56]…”