Value of cortical high-frequency gamma oscillations with electrocorticography in location of epileptogenic zone

Abstract

Objective To investigate the value of high-gamma oscillations (65~100 Hz) in epileptogenic foci localization by analyzing the intraoperative electrocorticography (ECoG) in patients with refractory temporal lobe epilepsy, along with comparing the occurrence rate and distribution characteristics of high-gamma activity as well as spike wave inside and outside the irritative zone and around the foci. Methods A retrospective analysis was carried out on the intraoperative ECoG data of 21 patients with refractory temporal lobe epilepsy in our hospital from January 2013 to January 2019. The channels with interictal epileptiform discharges (IEDs) were defined as irritated area, and those without IEDs as non-irritated area. Based on the preoperative imaging data, intraoperative navigation combined with neurosurgeon's judgment, the monitoring cortical area was divided into focal area, perifocal area and the area away from the focus. Then the occurrence rate and distribution characteristics of IEDs (filter range: 1~30 Hz) and high-gamma were compared, and the distribution of high-gamma activity inside and outside the irritated area, and the incidence of high-gamma around the foci were analyzed. Results ① The overall incidence of IEDs and of high-gamma in the 21 patients were both 100.0% (21/21), and the average number of channels for IEDs, high-gamma and gamma+IEDs was 9.50±2.80, 8.14±2.93 and 6.60±2.40, respectively, indicating notably more IEDs channels than the other 2, by RM one-way ANOVA (P < 0.05). ②The channel numbers of high-gamma were 6.60±2.40 and 1.50±1.30 in the irritated and non-irritated areas respectively, and the event rates were 0.42±0.30 and 0.20±0.20 respectively, showing significant difference between the 2 areas (P < 0.01). ③The event numbers of high-gamma activity were 46.00±42.00, 33.40±32.90 and 8.40±9.40 in the focal area, the perifocal area and the area away from the focus, respectively, with the corresponding event rate of 0.40±0.30, 0.37±0.38 and 0.10±0.10, respectively. There were no significant differences in the event numbers and rates between the focal and perifocal area, though they were both significantly higher than that of the area away from the focus, by paired t-test (P < 0.05). Conclusion Traditional IEDs of ECoG are still an important marker to guide the range of resection intra-operatively in epilepsy surgery, while high-gamma presents great consistency with both IEDs and foci, with more accurate identification of epileptogenic zone than IEDs. Therefore, IEDs combined with high-gamma may have greater value in the localization of epileptogenic zone.

Keywords

• electrocorticography
• epilepsy
• interictal epileptiform discharges
• high frequency oscillations
• epileptogenic zone