ABSTRACT
Objective To investigate the characteristic of theta oscillation in patients with frontal lobe epilepsy (FLE) by the analysis of multi-channel electroencephalographs (EEGs) during rest state and working memory(WM) maintenance. Methods The 19 FLE patients and 17 healthy subjects underwent EEG recording with 34-channel EEG machine during visual working memory task performance. The differences of behavioral results were analyzed between FLE group and controls. Short-time Fourier transform was used to calculate the power spectral density of different frequency bands in 34 channels. The theta power values during the retention period of working memory and rest state were compared between two groups. Results Compared with controls, reaction time of FLE increased significantly (P<0.01) and accuracy decreased (P<0.05). The power spectral density of theta band for FLE increased both in Fz and frontal region during rest state (P<0.01). Compared with controls, the power spectral density of theta oscillation decreased significantly in the frontal region for FLE during WM maintenance. Conclusion Our results suggest that working memory in patients with FLE was impaired. The absence of theta oscillation during the WM delayde period may provide a possible neural mechanism for the working memory dysfunction in FLE.
ABSTRACT
Objective To study the feature of theta oscillation during working memory (WM) dysfunction in patients with mild cognitive impairment (MCI). Methods Fifteen MCI patients (MCI group) and 15 healthy subjects for checkup (control group) in Tianjin Medical University General Hospital from January to November 2016 were recruited. The differences of behavioral results in visual WM tasks were compared between the two groups. Thirty four-channel electroencephalogram (EEG) signals were recorded simultaneously. Short-Time Fourier transform was used to calculate spatial and time-frequency distribution of power and spectral coherence of multi-channel EEGs. Results Compared with control group, MCI group showed significantly longer reaction time and lower accuracy in WM tasks (P<0.01). The analysis of EEGs revealed that the power of Fz channel was the biggest at frontal midline in both groups. And the power density of theta oscillation was lower at frontal electrode sites in MCI group than that of control group ( P<0.01), and theta coherence was significantly decreased in frontal region and between frontal-posterior regions ( P<0.05). Conclusion The absence of theta oscillaton in frontal region may be one of the important reasons of working memory dysfunction for MCI.
ABSTRACT
Objective Temporal lobe epilepsy (TLE),frequently accompanied by working memory dysfunction,is an important form of adult epilepsy syndrome.Study on neural mechanisms of TLE with working memory dysfunction has important scientific value and clinical significance.Theta oscillations are synchronous activity of the brain in the 4-8 Hz frequency range.It is well recognized that there is a close relationship between the theta oscillations and working memory behavior.TLE patients with working memory dysfunction were taken as the research subjects,and the theta oscillations absence in TLE with working memory behavioral disorder was carried out,which provide the reference for further research into the neural mechanisms of TLE with working memory dysfunction.Methods The 34-channel electroencephalographs (EEGs) were recorded from TLE group (18 TLE patients) and control groups (18 healthy subjects) while subjects were performing visual working memory (delayed matching-tosample) tasks.The EEGs during the 3 s delay period was analyzed as experimental data.Fourier transform was used to assess the EEGs spectrum.The channel with the strongest spectrum was selected as the feature channel.Short-time Fourier transform algosiths was employed to calculate the time-frequency representation of the feature channel for the TLE and control groups.Frequency band with the strongest spectrum was selected 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 Compared with the control group,the working memnory behavioral performance of the TLE group was lower:accuracy of the TLE group was significantly lower than that of the control group (P＜0.05),and reaction time of the TLE group was significantly longer than that of the control group (P＜0.001).The feature channel in working memnory was frontal midline (Fz) and the feature frequency band was theta band.The Fz spectrum of the feature frequency for TLE was lower than that for control (P＜0.05).The frontal spectrum (seven channels) of the feature frequency for TLE was lower than that of control (P＜0.01).Conclusions Theta oscillations for TLE with working memory behavioral disorder is absent,which maybe one of the possible neural mechanism of TLE with working memory dysfunction.
ABSTRACT
Objective The ability of working memory (WM) is to temporarily hold and manipulate information for cognitive tasks.The aim of this study was to investigate the causal flow distribution of multi-channel electroencephalographs (EEGs) during Sternberg visual WM task to help understand WM mechanism from the view of neural information transform.Methods Sixteen-channel EEGs were recorded from 8 healthy subjects during Sternberg task,total EEG data for 80 trials were recorded and preprocessed.The EEG powers for each channel were calculated via Fast Fourier transform (FFT).The feature channel was extracted based on the maximum power,and the feature frequency band for WM was determined by time-frequency analysis.The directed transfer function (DTF) and the value of causal flow in EEG feature frequency band were calculated.Results The EEG power focused on θ band (4-8 Hz) and at Fz channel.The maximum value of causal flow was located at Fz,and the first 4 maximum negative values of causal flow were at C3,C4,C5,C6.Conclusions The feature frequency band for WM is the θ band.The causal source (responsible region) is at Fz (frontal region) and the causal sinks are at C3,C4,C5,C6.
ABSTRACT
Objective Working memory (WM) is one of important cognitive functions.The aim of this study was to investigate spatial distributions of electroencephalographs (EEGs) power during visual WM task,which may provide support for studying the principal frequency band and critical region related to WM.Methods 32-channel EEGs were recorded from 16 healthy subjects while they perform visual WM task.The data came from 240 trials and the original EEGs were preprocessed.Fourier transform was applied to calculate spatial distributions of EEGs power in the δ,θ,α,β,γfrequency bands and the percentage of each band in the total power.Results The percentages of δ,θ,α,β,γbands in the total power were (22.44±0.86)％,(31.88±0.55)％,(24.66±1.43)％,(13.54±0.64)％,(7.47±0.48)％,respectively.The power in the θ band was significantly higher than those in the other bands (paired t-test,P＜0.001).The θ power was focused in the frontal midline region.Conclusions The principal frequency band related to WM was the θ band and the critical region was the frontal region.