Abstracts

Rationale: Cortical neuronal synchronization has been implicated to be an important mechanism driving the occurrence of epileptiform activity during sleep. This study aims to compare the change in background EEG phase synchronization during awake, N1, N2, N3 and REM sleep in patients with various types of epilepsies and healthy controls using ensemble measure. It also evaluates the role of AEDs in modulating EEG phase synchrony in patients with epilepsy. Methods: One hundred and twenty recruited patients with epilepsy were subdivided into 3 groups (N=40 in each group) [JME (age: 21.534.10 years; M: F = 20:20), TLE (age: 25.008.34 years; M: F = 22:18) and Extra-TLE (23.538.23 years; M: F = 20:20)] and 40 age, gender and BMI matched healthy controls (age: 23.854.91 years; M: F = 24:16) that were subjected to overnight polysomnography using 8-channel EEG. Each patient group was further subdivided into Drug naﶥ (N=20) and On Drug (N=20). EEG phase synchronization was performed using ensemble measure to compare phase synchronization indices (SI) during awake, N1, N2, N3 and REM sleep using 10-second artifact free, representative time windows from each stage in all subjects. SI was assessed for delta (d; 0.5-3Hz), theta (?; 4-7Hz), alpha (a; 8-12Hz) and beta (߻ 13-30Hz) frequency bands. The meanSD of SI during each stage were calculated and compared using 2-Way ANOVA followed by pairwise post-hoc comparison (p=0.05). Results: In delta band, there was progressive increase in SI from wake ?' N1 ?' N2 ?' N3 sleep stage, whereas SI in REM was comparable with that of wake. In theta band, SI tended to decrease in N2 and increase in N3. In alpha band, wake had the highest SI and the value decreased in N1, N2, N3 and REM (p < 0.001). In beta band, it was evident that there was a progressive increase in SI from wake ?' N1 ?' N2 ?' N3 sleep stages, whereas there was a decrease in SI during REM stage (p < 0.001). In both delta and theta bands, the SI was significantly more in patients with JME, TLE and Ex-TLE compared to controls, whereas in alpha and beta band, SI was comparable among patients and healthy controls. There was no difference in ensemble SI between drug naﶥ PWE and those on drug in any of the frequency bands. Conclusions: There was an increase in background cortical synchronization in patients with epilepsy compared to healthy controls in delta and theta frequency bands. However, background phase synchrony was comparable between drug naﶥ PWE and those on AEDs in all frequency bands, irrespective of wake or sleep stages. These findings implicate the role of cortical synchronization in influencing the occurrence of epileptic activity in an epileptic brain. Funding: Nil