Theta Oscillations Absence Of Working Memory Dysfunction In TLE

Temporal lobe epilepsy(TLE) is an important form of adult epilepsy syndrome. TLE is frequently accompanied by working memory dysfunction. Study on neural mechanisms of TLE with working memory dysfunction has important scientific value and clinical significance. Theta oscillations are synchronous activity in the brain in the 4-8Hz frequency range. It is well recognized that there is a close relationship between the theta oscillations and working memory behavior. Objective:TLE patients with working memory dysfunction were taken as the research subjects, we studied the neural mechanisms of theta oscillations absence in TLE with working memory behavioral disorder. Methods:34-channel electroencephalographs(EEGs) were recorded from 18 TLE patients and 18 healthy subjects, while they performed a visual working memory(delayed matching-to-sample) task. We analyzed the EEGs during the 3s delay period as experimental data. Fourier transform was used to assess the EEGs spectrum. The channel with the strongest spectrum was selected as the feature channel. We employed short-time Fourier transform to calculate the time-frequency representation of the feature channel for the TLE and control groups. We selected the frequency band with the strongest spectrum for control group as the feature frequency band in working memory. Then, the topographical maps of the feature frequency band spectrum were calculated for the TLE and control groups. Results:1. The clinical and demographic characteristics of subjects: 18 patients with TLE and 18 healthy controls completed the study. There were no significant differences between the two groups with respect to age, sex.2. Compared with control, the working memory behavioral performance of TLE was lower: the accuracy of TLE and control groups was 91.60 ± 0.93%,95.53 ± 1.23%(mean ± SEM) respectively, accuracy of TLE was significantly lower than that in control(P<0.05); the reaction time of TLE and control groups was 1004.59 ±18.37 ms,756.75 ± 11.67ms(mean ± SEM), reaction time of TLE was significantly longer than that in control(P<0.001).3. The feature channel in working memory is frontal midline(Fz)4. Time-frequency representations of the Fz channel for control suggested the feature frequency of working memory is theta band. The percent of power of 5 frequency band(delta(1~4Hz)、theta(4-8 Hz)、alpha(8-13 Hz)、beta(13-30Hz)、gamma(30-80 Hz))for control groups was 15.33±0.12%,32.65±0.24%,28.84±0.27%,16.33±0.18%,6.85±0.17% respectively, The percent of theta was the highest, and there were significant differences between the percent of theta with others(p<0.001). 5. The Fz spectrum of the feature frequency for TLE was lower than that for control(P<0.05). 6. The frontal spectrum(seven channels) of the feature frequency for TLE was lower than that for control(P<0.01). Conclusion: 1. TLE patients have working memory behavioral disorder. 2. The absence of theta oscillations is the possible neural mechanism for TLE with working memory behavioral disorder.