用有限元法计算媒质各向异性真实头模型脑电正问题

神经元所产生的脑内电活动通常可用电流源偶极子来模拟。讨论用有限元法计算电流源偶极子产生的电流与电位分布，推导出计算偶极子源在各向异性导电媒质中的有限元方程，并对其进行变形，使得在各向异性导电媒质中生成的有限元刚度阵对称。这一算法已应用于媒质各向异性的真实头模型脑电计算，得到了较为满意的结果。     

低频节律源传播方向对近真实头模型表面场电位动态参量的影响

θ振荡(4～8 Hz)是与学习、记忆等高级功能密切相关的低频脑节律,源于脑深处皮质区,头表面以额叶、颞叶最丰富。神经科学实验发现,该节律在脑内以一定方式传播,因成像技术局限和脑组织导电复杂性,其对头表面脑电节律的影响鲜有报告。依据等效偶极子电流源的脑电产生原理,以脑内低频单偶极子电流源(6 Hz正弦)偶极矩来仿真节律源驱动方向(以额叶为例定义指向),改变指向角度(以30°为移动单位),用有限元法计算电场,并对节律动态参量(大于平均值的显著能量、窄带相位)进行全局统计并对比。实验发现:脑内节律源在指向额叶表面传播时,几乎在所有指向角度下各向异性媒质会缩小显著能量空间;相反地,当源平行于额叶表面传播时,在所有指向角度下各向异性媒质会扩展显著能量空间,能量对源指向具有敏感性,而相位稳定性减小, 只与脑内节律源非线性相位时程有关,对该指向不敏感。结果表明,脑内低频节律源传播方向对头表面场电位动态参量作用不同。该研究为理解头表面低频节律动态参量提供电场计算依据,有助于理解脑内电活动、脑组织导电特性和头表面场电位动态参量之间的映射关系。     

Gabor小波变换和希尔伯特变换研究海马区癫痫发作间期尖波对theta振荡能量特性的影响

背景：Theta振荡是海马区神经活动具有代表性的特征,也是从更为微观领域研究癫痫与认知关系的重要切入点。 目的：分析海马区癫痫发作间期尖波对Theta振荡能量特性的影响。 方法：采用法国马赛地中海大学医学院提供的8只致痫大鼠和10例患者脑电数据,同时采集相应致痫大鼠在注射致痫药物无发作间期尖波出现时的脑电数据作对照。利用Gabor小波变换和希尔伯特变换分别提取Theta振荡在尖波作用前、后的能量,并将这两种方法提取Theta振荡能量的结果进行比较。 结果与结论：癫痫组Theta能量动态特性：癫痫发作间期尖波削弱了Theta振荡能量,而在经历癫痫发作间期后的较长时间,Theta振荡能量得到恢复。推测脑默认网络的连接强度受到癫痫状态的影响,存在变弱的可能。而默认网络的减弱,是认知功能下降的一种病理基础。     

阿尔兹海默症转基因鼠生长过程中海马theta节律及行为学的实验研究

研究阿尔兹海默症(Alzheimer's disease,AD)转基因鼠(5XFAD)认知功能障碍与海马神经节律的关系,探讨海马theta节律在AD发展过程中的变化。设计AD转基因鼠和同源WT鼠在2月龄和5月龄的水迷宫及在体电生理实验,分析对比AD鼠和WT鼠行为学表现及海马theta节律频谱特征。AD鼠和WT鼠在2月龄时行为学表现无差异,AD鼠相较于WT鼠theta节律主频降低;在5月龄时,AD鼠出现明显的运动障碍和认知障碍,theta节律能量降低。结果表明,AD疾病发展过程中,海马神经节律的异常要先于认知功能障碍。研究结果为通过神经调控延缓AD认知障碍提供了实验依据。     

基于声换能器特性的磁感应磁声成像正问题分析

目的在考虑声换能器特性的基础上,对磁感应磁声成像的正问题进行研究,并探讨其声源的产生、传播及接收机制。方法参考CT的三维Phantom仿真模型建立磁感应磁声成像正问题的模型,并结合电磁场理论利用有限元软件comsol仿真分析模型内部电导率分布与磁场和磁感应电场的关系,得到模型内部的磁感应电流分布。然后再深入研究声偶极子模型,并检测分析声换能器的特性后,给出相应的仿真声信号检测结果。结果磁感应电流密度在中心位置处为0,在电导率边界处变化较大,声换能器的检测声场分布和声偶极子传播的指向性会极大的影响声换能器接收到的磁声信号的值。结论为磁感应磁声成像实验研究及由声信号重建物体内部的电导率分布提供理论基础。     

海马区神经电信号相位同步化的初步研究

大脑各个区域的神经电活动存在各种不同频率的振荡,而theta节律振荡(5～10 Hz)是海马区神经活动具有代表性的特征.本文用海马区theta节律显著性检测和theta节律相位同步化的方法来分析多电极记录的神经元放电及其局部场电位信号,验证了theta节律成分的显著性和动物行为之间的关系,并首次研究了小鼠在不同行为状态下左右海马神经电活动之间的相位同步化的差异.     

新型各向异性组织介电特性在体测量射频探头仿真研究

本文提出了一种新型探头设计方案。该探头可通过一次操作,完成射频段各向异性的生物组织其介电特性在正交方向上的在体测量。通过仿真实验,本文在1~1 000 MHz频段内针对探头尺寸参数对极板间能量耦合度和探头测量灵敏度的影响进行了研究。针对该频段内的实际测量需求,给出了探头的具体设计方案,并验证了该探头的测量效果。仿真结果显示,在200~400 MHz内,该探头能够将极板间能量耦合度控制在–12 d B以下,并能保持对各向异性生物组织其介电特性的测量具有较高的灵敏度。仿真结果表明,该探头在射频段内对各向异性的生物组织其介电特性有良好的测量能力,避免了传统测量方法因多次操作而造成的测量误差,为各向异性的生物组织其介电特性在体测量技术研究提供了新思路。     

基于乳腺肿瘤模型的感应式磁声成像正问题研究

感应式磁声成像(MAT-MI)是一种融合磁感应技术和超声断层扫描技术的新型生物电阻抗成像方法,兼具电阻抗成像高对比度和超声断层扫描技术高空间分辨率的优点。本研究结合电磁场理论推导了MAT-MI在电导率均匀媒质内部和电导率发生突变的两种不同媒质分界面上的声源计算公式,揭示了MAT-MI声源与电导率的关系。模拟物理环境构建三维柱状线圈和乳腺肿瘤模型,借助有限元分析软件ANSYS进行时变电磁场分析,并应用电磁场有限元分析的结果,计算乳腺和肿瘤内部及边界的声激励源分布,应用自由空间波动方程格林函数解计算MAT-MI空间声场分布。仿真结果表明,所推导的计算公式能够直接应用电磁场有限元分析的结果,有效地计算乳腺肿瘤模型的声源和空间声场分布,MAT-MI将是乳腺肿瘤早期筛查、检测和诊断的一种潜在的和有效的医学辅助手段。     

由水分子扩散张量计算脑组织电导率张量的新方法

脑组织电导率在脑电/磁研究中是一个重要参数.为了获取脑组织电导率,本研究利用扩散张量成像(DTI)技术,从电化学角度出发,提出了基于Stokes-Einstein与Nernst-Einstein方程的计算脑组织电导率的一种新方法,以三个正交方向上的电导率作为不同脑组织的电导率张量特征值.在人体头部DTI数据上进行计算,并与不同脑组织(白质、灰质、脑脊液)的经验电脑率值进行了对比,发现扩散各向异性越严重的组织,其电导率张量特征值偏离经验值越远,进一步证明了在脑电,磁计算中要考虑脑组织电导率各向异性的必要性.所提出的方法,基于扩散张量,考虑脑液体中各种离子浓度等因素,为获取脑组织各向异性电导率分布提供了一种新的有效途径.     

蛙血细胞被动电生理特性的数据分析

在10^4-10^8Hz范围内,应用阻抗测量技术研究了蛙血液细胞的介电常数,电导率与电场频率的关系特性,利用细胞介电谱,Cole-Cole图,介电损失和损耗角正切分析了蛙血液细胞的被动电生理特性的数据特征,结果表明：蛙全血细胞具有两个特征频率,第一特征频率fci在10^5Hz范围内,第二特征频率fc2在10^6Hz范围内。     

Age Distribution of MEG Spontaneous Theta Activity in Healthy Subjects

No HeadingSummary: This study investigates the possible relevance of distribution and age variation of spontaneous theta activity (4–8 Hz) in normal subjects using magnetoencephalography (MEG) recordings. Spontaneous theta was recorded with a 151-channel MEG in healthy subjects; moreover, in a group of 10 subjects, simultaneous MEG-EEG was recorded in order to compare the two methods. Theta was divided in two sub-bands: TA (4–6 Hz) and TB (6–8 Hz). The pre-processed data were transformed into the frequency domain by Fast Fourier Transform (FFT)-based software by subdividing the data in epochs of 5 sec, on which FFT amplitudes are computed. Moreover, on all trials a simple model of a single electric current embedded in a spherically symmetric conductor was fitted automatically to the magnetic fields and projected onto an averaged MRI. The results obtained show that FFT-based theta power spectrum was distributed in adults with the highest power over the posterior parietal and occipital areas with TB dominance. The dipole analysis resulted in a mid-sagittal distribution, though the youngest group displayed theta dipoles fitting more posteriorly respect to the adults and the elderly. These results suggest that spontaneous theta activity is a diffuse and pervasive rhythm which shows some different topographical distribution among the age groups. Whether the prevalent posterior distribution of theta is the expression of distinct networks or the outcome of complex dynamics are questions of possible relevance in the organization of higher order processes.     

Neural basis of implicit motor sequence learning: Modulation of cortical power

Implicit sequence learning describes the acquisition of serially ordered movements and sequentially structured cognitive information, that occurs without awareness. Theta, alpha and beta cortical oscillations are present during implicit motor sequence learning, but their role in this process is unclear. The current study addressed this gap in the literature. A total of 50 healthy adults aged between 19 and 37 years participated in the study. Implicit motor sequence learning was examined using the Serial Reaction Time task where participants unknowingly repeat a sequence of finger movements in response to a visual stimulus. Sequence learning was examined by comparing reaction times and oscillatory power between sequence trials and a set of control trials comprising random stimulus presentations. Electroencephalography was recorded as participants completed the task. Analyses of the behavioral data revealed participants learnt the sequence. Analyses of oscillatory activity, using permutation testing, revealed sequence learning was associated with a decrease in theta band (4–7 Hz) power recorded over frontal and central electrode sites. Sequence learning effects were not observed in the alpha (7–12 Hz) or beta bands (12–20 Hz). Even though alpha and beta power modulations have long been associated with executing a motor response, it seems theta power is a correlate of sequence learning in the manual domain. Theta power modulations on the serial reaction time task may reflect disengagement of attentional resources, either promoting or occurring as a consequence of implicit motor sequence learning     

Spectral analysis of hippocampal slow wave activity during feeding and drinking in the rabbit

The dorsal hippocampal electrical activity was recorded in rabbits and correlated with discrete components of consummatory responses during drinking and eating, as well as during immobile attention. Power-spectral and autocorrelation analyses revealed that chewing was accompanied by two dominant frequencies, one of low power from 0.5 to 3.0 Hz, and one in the theta range of relatively low power and frequency. Theta rhythms accompanied all other components of ingestive behavior, with an increasing order of frequencies from licking of water, eating of liquid food, biting of solid foods, to immobile attention, whereas power of theta remained invariant across these conditions.     

Clinical implications of quantitative electroencephalography and current source density in patients with Alzheimer's disease

This study examined whether quantitative electroencephalography (qEEG) and current source density (CSD) can be used to evaluate symptom severity in Alzheimer's disease (AD) patients. Thirty AD patients (13 mild and 17 moderate severity) and 30 normal control (NC) subjects were recruited. The Korean version of the Consortium to Establish a Registry for Alzheimer's Disease Assessment Packet and the Global Deterioration Scale were measured. qEEG and CSD data were analyzed in five frequency bands: delta (1-3?Hz), theta (4-7?Hz), alpha (8-12?Hz), beta (13-25?Hz), and gamma (30-50?Hz). Compared with the NC subjects, the moderate AD patients had significantly increased theta and decreased beta power. Compared with the mild AD patients, the moderate AD patients had significantly decreased beta power. In the AD patients, the theta power was significantly correlated with a poor performance for global cognition; however, beta power was positively correlated with a good performance for global cognition, attention, memory, visuospatial function, and executive function. The CSD of the theta band in the superior temporal gyrus, transverse temporal gyrus, insula, postcentral gyrus, cuneus, and lingual gyrus was significantly different between NC subjects and moderate AD patients and between mild and moderate AD patients. The theta CSD of these regions was significantly correlated with a poor performance for global cognition, memory, visuospatial function, execution, and language. The results suggest that qEEG and the CSD of the theta and beta bands are useful biological markers in AD patients.     

Hippocampal network patterns of activity in the mouse

Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6-9 Hz) and gamma (40-100 Hz) oscillations were present during exploration and rapid eye movement sleep. Gamma power and theta power were comodulated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consummatory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140-200-Hz "ripples" in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude "dentate spikes" occurred in association with increased discharge of hilar neurons. The amplitude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse and rat.     

Septotemporal variation in dynamics of theta: speed and habituation

Theta (6-12 Hz) field potentials and the synchronization (coherence) of these potentials present neural network indices of hippocampal physiology. Theta signals within the hippocampal formation may reflect alterations in sensorimotor integration, the flow of sensory input, and/or distinct cognitive operations. While the power and coherence of theta signals vary across lamina within the septal hippocampus, limited information is available about variation in these indices across the septotemporal (long) or areal axis. The present study examined the relationship of locomotor speed to theta indices at CA1 and dentate gyrus (DG) sites across the septotemporal axis as well as in the entorhinal cortex. Our findings demonstrate the dominant relationship of speed to theta indices at septal sites. This relationship diminished systematically with distance from the septal pole of the hippocampus at both CA1 and DG sites. While theta power at entorhinal sites varied in relation to speed, there were no differences across the areal axis of the entorhinal cortex. Locomotor speed was also related to changes in theta coherence along the septotemporal axis as well as between the hippocampus and entorhinal cortex. In addition to the speed-related variation, we observed a decrease in theta power at more temporal hippocampal sites over repeated behavioral testing within a single day that was not observed at septal sites. The results outline a dynamic and distributed pattern of network activity across the septotemporal axis of the hippocampus in relation to locomotor speed and recent past experience.     

Comparison of the effects of acute and chronic administration of ketamine on hippocampal oscillations: relevance for the NMDA receptor hypofunction model of schizophrenia

The proper organization and function of GABAergic interneuron networks is essential for many cognitive processes and abnormalities in these systems have been documented in schizophrenic patients. The memory function of the hippocampus depends on two major patterns of oscillations in the theta and gamma ranges, both requiring the intact functioning of the network of fast-firing interneurons expressing parvalbumin. We examined the ability of acute and chronic administration of NMDA receptor (NMDA-R) antagonists to recapitulate the oscillatory dysfunctions observed in schizophrenia. In freely moving rats, acute injection of MK801 or ketamine increased gamma power in both CA1 and dentate gyrus of the hippocampus. Theta peak shifted to higher frequencies whereas the average 5–10 Hz theta power decreased by 24% in CA1 and remained high in the dentate gyrus. Strong increase in CA1 gamma and decrease in theta power triggered by brainstem stimulation were found under urethane anesthesia. In contrast to acute experiments, chronic administration of ketamine caused a steady decline in both gamma and theta oscillations, 2–4 weeks after treatment. A further important difference between the two models was that the effects of acute injection were more robust than the changes after chronic treatment. Chronic administration of ketamine also leads to decrease in the number of detectable parvalbumin interneurons. Histological examination of interindividual differences indicated, however, that within the ketamine treated group a further decrease in parvalbumin neurons correlated with strengthening of oscillations. The findings are consistent with abnormalities of oscillations in human schizophrenia and further validate the NMDA-R hypofunction hypothesis.     

Semantic priming increases left hemisphere theta power and intertrial phase synchrony

Information is stored in distributed cortical networks, but it is unclear how distributed stores are synthesized into a unified percept. Activation of local circuits in the gamma range (30 < < 80 Hz), and distributed stores in the low theta range (3–5 Hz) may underlie perceptual binding. Words have a crucial role in semantic memory. Within memory, the activation of distributed semantic stores is facilitated by conceptually related previous items, termed semantic priming. We sought to detect event‐related brain oscillations (EROs) sensitive to semantic activation and priming. Here, we show that low theta evoked power and intertrial phase locking (4–5 Hz) from 250–350 msec over left hemisphere language areas was greater to related than to unrelated words. Theta band event‐related oscillations over left hemisphere language areas may provide a brain signature for semantic activation across distributed stores being facilitated by semantic priming.     

Decomposing delta, theta, and alpha time-frequency ERP activity from a visual oddball task using PCA.

OBJECTIVE: Time-frequency (TF) analysis has become an important tool for assessing electrical and magnetic brain activity from event-related paradigms. In electrical potential data, theta and delta activities have been shown to underlie P300 activity, and alpha has been shown to be inhibited during P300 activity. Measures of delta, theta, and alpha activity are commonly taken from TF surfaces. However, methods for extracting relevant activity do not commonly go beyond taking means of windows on the surface, analogous to measuring activity within a defined P300 window in time-only signal representations. The current objective was to use a data driven method to derive relevant TF components from event-related potential data from a large number of participants in an oddball paradigm. METHODS: A recently developed PCA approach was employed to extract TF components [Bernat, E. M., Williams, W. J., and Gehring, W. J. (2005). Decomposing ERP time-frequency energy using PCA. Clin Neurophysiol, 116(6), 1314-1334] from an ERP dataset of 2068 17 year olds (979 males). TF activity was taken from both individual trials and condition averages. Activity including frequencies ranging from 0 to 14 Hz and time ranging from stimulus onset to 1312.5 ms were decomposed. RESULTS: A coordinated set of time-frequency events was apparent across the decompositions. Similar TF components representing earlier theta followed by delta were extracted from both individual trials and averaged data. Alpha activity, as predicted, was apparent only when time-frequency surfaces were generated from trial level data, and was characterized by a reduction during the P300. CONCLUSIONS: Theta, delta, and alpha activities were extracted with predictable time-courses. Notably, this approach was effective at characterizing data from a single-electrode. Finally, decomposition of TF data generated from individual trials and condition averages produced similar results, but with predictable differences. Specifically, trial level data evidenced more and more varied theta measures, and accounted for less overall variance.     

Manifest sleepiness and the spectral content of the EEG during shift work

Twenty-five three-shift workers in a process industry were subjected to ambulatory polysomnography during one afternoon and one night shift. The electroencephalographic (EEG) recordings were analyzed with spectral analysis. Subjective sleepiness increased during the night work but did not reach an extreme level. Five subjects fell asleep during night work and the involuntary naps were preceded by a few minutes of increased alpha (8-11.9 Hz) power density. Alpha and theta activity occurred in very short bursts. The hourly mean EEG alpha power density increased significantly but moderately during the night shift and correlated with subjective ratings of sleepiness. Theta power density (4-7.9 Hz) did not increase during the night shift, nor did it correlate with subjective sleepiness. It was suggested that the shift workers could prevent much of the polysomnographic manifestations of sleepiness by various types of activity (including succumbing to sleep). It was also suggested that averaging power density values across long time periods might not be an optimal strategy for detection of sleepiness, but rather some method of emphasizing the occurrence of alpha or theta bursts.