epileptic high - frequency activity includes pathological activities with frequency above 80 hz recorded in epileptic brains in vitro , in animal models and in patients . isolated high - frequency oscillatory events are the most common type of high - frequency activity and are called high - frequency oscillations ( hfos ) . hfos include ripples ( 80250 hz ) and fast ripples ( frs ) ( 250500 hz ) . only events containing at least 4 consecutive oscillations above 80 hz were regarded as hfos . it has been proposed that hfos are related to the epileptic attack by animal trial . recent studies suggest the changes of hfos in epileptic brains are related to epileptogenesis and seizure genesis . the characteristics of hfos in mesial temporal epileptic patients during ictal and interictal periods have been well studied . our study focused on neocortical epileptic patients who were seizure - free after surgery with normal magnetic resonance imaging ( mri ) before surgery avoiding the influence of hfos by other lesions . the seizure onset zones ( soz ) of the patients should be verified by the consequences of surgery . the removal of areas with hfos seems to predict effective surgical interventions . between december 2010 and january 2012 , 18 patients with implanted subdural electrodes for epilepsy surgery evaluation were recorded at a sampling rate of 1600 hz in our epilepsy center . patients with a proven neocortical epilepsy and normal mri before surgery were included in this study . besides , we only selected patients that were seizure - free for more than 1-year after surgery . other patients were excluded because of three reasons : abnormal mri before surgery , still with seizures after surgery , not neocortical epilepsy . clinical and electrophysiological data of four patients vpa : sodium valproate ; cbz : carbamazepine ; ltg : lamotrigine ; tpm : topiramate ; lev : levetiracetam ; oxc : oxcarbacepine ; b : bilateral ; l : left ; r : right ; f : frontal lobe ; t : temporal lobe ; p : parietal lobe ; smf : superior and middle frontal gyrus ; mif : middle and inferior frontal gyrus ; pnt : posterior of neocortical temporal lobe ; df : dorsolateral frontal lobe ; aed : anti - epileptic drug . patients were implanted subdural electrodes according to clinical history , seizure semiology and surface electroencephalogram ( eeg ) investigations . the electrodes have a 2.5 mm stainless steel central core , with a 10 mm interconnecting distance . the ecog was sampled by a 128-channel grass / twins monitoring system ( grass technologies , usa ) at the sampling rate of 1600 hz with low - frequency cut of 0.1 hz and high - frequency cut of 500 hz . the ecog was recorded for 314 days constantly in order to acquire at least three seizures to orient the epileptogenic zone . the data were visually inspected , and channels with artifacts were removed . in total , at last 295 channels of the ecog were analyzed . interictal data imply that there was no seizure within 1 h before and after the selected section for each individual patient . for preictal period , 3 the ecog data were transformed to european data format form in order to be read by the analysis software . ripples and frs were analyzed by advanced source analysis ( asa ) ( asa , the netherlands ) software . at last , 295 channels were analyzed including 39 channels from soz and 256 channels from nonseizure onset zones ( nsoz ) . the soz was identified as the area showing the earliest eeg change ( ictal discharge ) from baseline prior to or concomitant with clinical onset . ripples were analyzed with a filter from 80 to 250 hz at the computer screen resolution ratio 1280 ( 0.8 s / page , 100 v / cm ) . frs were analyzed with 250 and 500 hz filters at the computer screen resolution ratio 1280 ( 0.5 s / page , 30 v / cm ) . the accurate starting and ending point and the numbers of hfos can be read from the asa [ figure 1 ] . ripple ( a ) and fast ripple ( b ) analyzed by advanced source analysis . multiple comparison of rank sum test was used to compare the average duration of ripples and frs inside and outside the soz . between december 2010 and january 2012 , 18 patients with implanted subdural electrodes for epilepsy surgery evaluation were recorded at a sampling rate of 1600 hz in our epilepsy center . patients with a proven neocortical epilepsy and normal mri before surgery were included in this study . besides , we only selected patients that were seizure - free for more than 1-year after surgery . other patients were excluded because of three reasons : abnormal mri before surgery , still with seizures after surgery , not neocortical epilepsy . clinical and electrophysiological data of four patients vpa : sodium valproate ; cbz : carbamazepine ; ltg : lamotrigine ; tpm : topiramate ; lev : levetiracetam ; oxc : oxcarbacepine ; b : bilateral ; l : left ; r : right ; f : frontal lobe ; t : temporal lobe ; p : parietal lobe ; smf : superior and middle frontal gyrus ; mif : middle and inferior frontal gyrus ; pnt : posterior of neocortical temporal lobe ; df : dorsolateral frontal lobe ; aed : anti - epileptic drug . patients were implanted subdural electrodes according to clinical history , seizure semiology and surface electroencephalogram ( eeg ) investigations . the electrodes have a 2.5 mm stainless steel central core , with a 10 mm interconnecting distance . the ecog was sampled by a 128-channel grass / twins monitoring system ( grass technologies , usa ) at the sampling rate of 1600 hz with low - frequency cut of 0.1 hz and high - frequency cut of 500 hz . the ecog was recorded for 314 days constantly in order to acquire at least three seizures to orient the epileptogenic zone . the data were visually inspected , and channels with artifacts were removed . in total , at last 295 channels of the ecog were analyzed . interictal data imply that there was no seizure within 1 h before and after the selected section for each individual patient . for preictal period , the ecog data were transformed to european data format form in order to be read by the analysis software . ripples and frs were analyzed by advanced source analysis ( asa ) ( asa , the netherlands ) software . at last , 295 channels were analyzed including 39 channels from soz and 256 channels from nonseizure onset zones ( nsoz ) . the soz was identified as the area showing the earliest eeg change ( ictal discharge ) from baseline prior to or concomitant with clinical onset . ripples were analyzed with a filter from 80 to 250 hz at the computer screen resolution ratio 1280 ( 0.8 s / page , 100 v / cm ) . frs were analyzed with 250 and 500 hz filters at the computer screen resolution ratio 1280 ( 0.5 s / page , 30 v / cm ) . the accurate starting and ending point and the numbers of hfos can be read from the asa [ figure 1 ] . ripple ( a ) and fast ripple ( b ) analyzed by advanced source analysis . multiple comparison of rank sum test was used to compare the average duration of ripples and frs inside and outside the soz . statistical significance was set at p < 0.05 . ad : the average duration of hfo ; pt : the permillage time occupied by hfos ; soz : seizure onset zones ; nsoz : nonseizure onset zones ; hfos : high - frequency oscillations . ad : the average duration of hfos ; pt : the permillage time occupied by hfos ; frs : fast ripples ; soz : seizure onset zones ; nsoz : nonseizure onset zones ; hfos : high - frequency oscillations . the average duration of every ripple in the soz was longer than that in the nsoz during interictal periods ( z = 6.94 , p < 0.001 ) . during the preictal periods , there was no different between in soz and nsoz ( z = 1.44 , p = 0.075 ) . the average duration of every frs inside the soz were shorter than that outside the soz during both interictal ( z = 7.16 , p < 0.001 ) and preictal periods ( z = 2.35 , p = 0.009 ) . during interictal period , the pt of frs in soz is more than 20 times than that in nsoz . and during the preictal period , the pt of frs in soz is about 67 times than that in nsoz . for ripples , the permillage time occupied by hfos was 0.83 in nsoz and 1.17 in soz during the interictal period . during preictal period for frs , the permillage time occupied by hfos was 0.02 in nsoz and 0.42 in soz during the interictal period . during preictal period , they were 0.03 in nsoz and 2 in soz . the average duration of every ripple in the soz was longer than that in the nsoz during interictal periods ( z = 6.94 , p < 0.001 ) . during the preictal periods , there was no different between in soz and nsoz ( z = 1.44 , p = 0.075 ) . the average duration of every frs inside the soz were shorter than that outside the soz during both interictal ( z = 7.16 , p < 0.001 ) and preictal periods ( z = 2.35 , p = 0.009 ) . during interictal period , the pt of frs in soz is more than 20 times than that in nsoz . and during the preictal period , the pt of frs in soz is about 67 times than that in nsoz . for ripples , the permillage time occupied by hfos was 0.83 in nsoz and 1.17 in soz during the interictal period . during preictal period , they were 2.02 in nsoz and 7.93 in soz . for frs , the permillage time occupied by hfos was 0.02 in nsoz and 0.42 in soz during the interictal period . during preictal period , they were 0.03 in nsoz and 2 in soz . our results indicate that hfos links to soz in patients with neocortical epilepsy without a visible lesion on mri . the study selected patients with normal mri in order to avoid the influence of hfos by other lesions . all our patients were seizure - free proved that the removed areas included the epileptogenic tissue . the percentage of occupancy by hfos in the soz - channels was significantly higher than that in the nsoz - channels . this increase was seen in ripples and frs , especially frs . during interictal period , the pt of frs in soz is more than 20 times than that in nsoz . and during the preictal period , the pt of frs in soz is about 67 times than that in nsoz . nevertheless , the percentage of time occupied by hfos in this study is less than zijlmans study . second , zijlmans selected 10 s before seizure onset while we analyzed 3 m before seizure onset and hfos tend to increase before seizure onset . third , zijlmans chose chronic sleep stage as the interictal period that usually showed more epileptiform discharge in patients . although frs have been more strongly linked to epileptogenesis than ripples , we found that both were increased in the soz . the percentage of occupancy by hfos in the soz - channels was significantly higher than that in the nsoz - channels , especially frs . frs proved to be a reliable epileptogenic marker since they were closely related to soz . ripples are considered to play an important role in information processing , and consolidation of memory , which are thought as physiological hfo the distinction between physiological and pathological hfo has remained unclear . recently , it was showed that pathological hfo had higher mean spectral amplitude , longer mean duration , and lower mean frequency than physiological - induced hfo . frs represent field potentials of population spikes from clusters of abnormal synchronously bursting neurons , in contrast to ripples , which represent field potentials of summated inhibitory postsynaptic potentials . the average duration of every frs was shorter in soz than in nsoz during both interictal and preictal period . maybe neurons producing the frs focused on a limited area may cause shorter average duration in the soz . more and more burst of hfos , especially frs , means the onset of seizures .
background : to study the characters of high - frequency oscillations ( hfos ) in the seizure onset zones ( soz ) and the nonseizure onset zones ( nsoz ) in the electrocorticography ( ecog ) of patients with neocortical epilepsy.methods:only patients with neocortical epilepsy who were seizure - free after surgery as determined with ecog were included . 
 we selected patients with normal magnetic resonance imaging before surgery in order to avoid the influence of hfos by other lesions . 
 three minutes preictal and 10 min interictal ecog as recorded in 39 channels in the soz and 256 channels in the nsoz were analyzed . 
 ripples and fast ripples ( frs ) were analyzed by advanced source analysis software ( asa , the netherlands ) . 
 average duration of hfos was analyzed in soz and nsoz separately.results:for ripples , the permillage time occupied by hfos was 0.83 in nsoz and 1.17 in soz during the interictal period . during preictal period , they were 2.02 in nsoz and 7.93 in soz . 
 for frs , the permillage time occupied by hfos was 0.02 in nsoz and 0.42 in soz during the interictal period . during preictal period , they were 0.03 in nsoz and 2 in soz.conclusions:high-frequency oscillations are linked to soz in neocortical epilepsy . 
 our study demonstrates the prevalent occurrence of hfos in soz . 
 more and more burst of hfos , especially frs , means the onset of seizures .