The Study Of The Theta Oscillation Characteristic For Working Memory In Frontal Lobe Epilepsy

Objective Frontal lobe epilepsy(FLE)is a common subtype of epilepsy,representing 15% of refractory epilepsy.About 21%~67% of the epileptic patients suffer from cognitive dysfunction,of which working memory(WM)impairment is the most important clinical manifestation.The dysfunction of WM influences the treatment and quality of life for patients with FLE.Theta oscillation that was generated mainly by prefrontal cortex was very important to process information of WM.This study aimed to investigate the characteristic of theta oscillation in patients with FLE by the analysis of multi-channel electroencephalographs(EEGs)during rest state and WM maintenance,so that to explore the possible neuromechanism of working memory dysfunction in FLE and provide the theoretical support to treat the cognitive dysfunction for FLE.Methods 1.In this study,19 patients with FLE recruited from the Epilepsy Clinic of the Department of Neurology of Tianjin Medical University General Hospital were enrolled in this study.As control group,17 healthy volunteers whose age,sex and other aspects matched with the patients participated our study.All the subjects performed a visual working memory task(delayed matching-to-sample task).The averaged reaction time and accuracy were calculated to evaluate WM behavior,and the differences of behavioral results were analyzed between FLE and controls.2.The subjects underwent EEG recording with 34-channel EEG machine during the rest state and visual working memory task performance.Then it's necessary to pre-process the original EEGs signal by removing the power frequency interference,base line excursion,ocular and muscle artifacts.3.The averaged power spectral density of the different power spectra in 34 channels were calculated by analyzing time-frequency via short-time Fourier transform.The power percentage of the five frequency band were compared to confirm the feature frequency and the topographical maps of the averaged power were analyzed to select the typical channel.The differences of the theta power in feature channel and brain region were analyzed during the maintenance phase of WM and rest state between the controls and patients with FLE.4.The comparisons of general information between patients with FLE and the controls were analyzed by single sample t-test and Fisher exact probability.The results of WM task and the power spectral density of theta band between the two sets of subjects were compared with single sample t-test.The comparation among percentage of the power spectral density in the five frequency bands were analyzed by one-way ANOVA and the multiple comparison between groups were applied LSD-t test.The results were shown as mean ± SEM and P<0.05 meant that the difference was statistically significant.Results1.The reaction time of the patients with FLE and controls were 944.51±31.90 ms and 723.12±43.46 ms.The accuracy of the patients and controls were 92.67±1.14% and 95.96±0.92%.Compared with controls,the patients with FLE performed badly in the WM tasks: reaction time of FLE increased significantly(P<0.001)and accuracy decreased obviously(P<0.05).2.During rest state,the theta power in Fz for FLE and controls were 1.9979±0.1018uV~2/Hz and 0.5410±0.0053uV~2/Hz,the power spectral density of theta band in frontal region for FLE and controls were 1.4553±0.0733uV~2/Hz,0.3898±0.0034uV~2/Hz.Compared with controls,the power spectral density of theta band for FLE increased both in Fz and frontal region during rest state(P<0.001).3.Compared with controls,the power spectral density of theta oscillation decreased significantly in the frontal region for FLE during WM maintenance.Conclusions1.The patients with FLE suffered from working memory dysfunction,performed as that the reaction time increased and accuracy declined.2.The reduction of theta oscillation during the delayed period of WM may provide a possible neural mechanism for the working memory dysfunction in FLE.3.The increase of theta oscillation in FLE during rest state may lead to the decline of theta oscillation on the working memory delayed period.