运动想象脑电的ERD/ERS分析

脑电信号所包含的频率分量及其变化规律是脑-计算机接口(brain- computer interface,BCI)研究的关键之一.事件相关去同步(event- ralated desynchronization,ERD)/同步现象(event- related synchronization,ERS)则是确定EEG频带的基本方法.本文在事件相关现象的神经生理学原理的基础上,利用传统计算方法,提出简单而有效的ERD/ERS波形的拓扑图法;并且对比应用基于匹配追踪法的分解参数,采用平均时间-频率能量分布图的方法,研究ERD/ERS规律.分析实际运动想象脑电MI-EEG时,两种方法的结论可以互相验证,也体现了各自的优点.     

一种运动想象脑电分类算法的研究

为了解决脑机接口(BCI)中不同意识任务下脑电信号分类问题,针对运动想象脑电(EEG)的事件相关去同步/同步(ERD/ERS)现象,提出一种基于支持向量机(SVM)的实用分类算法。该算法首先对脑电信号进行滤波,获得对运动想象比较敏感的频段,对滤波后的脑电信号,通过去均值减小由于均值不同所造成的误差,然后,再提取基于ERD/ERS的脑电能量场强特征,对提取的特征,运用支持向量机(SVM)进行分类,得到了满意的效果。结果表明,此方法可为脑机接口技术的应用提供有效的手段。     

基于改进CSP算法的运动想象脑电信号识别方法

针对想象运动的脑机接口(BCI)系统中,在电极导联数少的情况下存在脑电信号分类准确率降低的问题,提出一种改进共同空间模式(CSP)算法. 通过对事件相关去同步(ERD)/事件相关同步(ERS)生理现象较明显的频段进行滤波, 选取最大特征值对应的表征运动想象脑电信号状态的最优特征向量,进而提出特征向量新的定义方法,同时与支持向量机(SVM)相结合,实现运动想象脑电数据的分类.对于GRAZ大学提供的运动想象脑电数据(Data Ⅲ),想象左手运动脑电信号的识别准确率为98.57%.想象右手运动的脑电识别率为100%.实验结果表明,改进的CSP算法更准确地反映脑电信号的任务状态,有效避免了特征模式的重复选取问题,具有更优的分类性能.     

多模式刺激下运动想象脑电信号的特征调制研究

事件相关去同步(ERD)现象是脑电信号的基本特征,以ERD特征分析为基础的运动想象脑–机接口在运动功能康复方面具有重要意义。能否有效提取脑电信号中的ERD特征是决定脑–机接口性能的关键,因此研究受试者何种刺激模式下会产生明显的ERD特征至关重要。本文试验设计了4种不同的刺激模式(静态文字刺激、抓握视频刺激、手指序列运动视频刺激以及带声音的手指序列运动视频刺激),并分析了这几种刺激模式下的ERD特征。综合时频图谱、功率谱曲线、ERD值和脑地形图分析结果发现,手指序列运动视频刺激和带声音的手指序列运动视频刺激模式下,激发的ERD特征程度更深、范围更广,在以ERD特征分析为基础的脑–机接口的实际应用中也会有更好的效果,也可以在一定程度上提高脑–机接口系统使用者的认可度和接受度。     

基于脑电复杂度的意识任务的特征提取与分类

本研究提出了利用事件相关脑电复杂度提取大脑运动意识特征，应用Mahalanobis距离判别式分析法，对人脑想象左右手运动任务进行分类，获得了满意的结果。对受试者想象左右手运动期间在大脑初级感觉运动皮层区记录的脑电信号采用复杂度分析方法量化了事件相关去同步（ERD）和事件相关同步（ERS）时程，结果表明EEG复杂度特征较好反映了ERD／ERS变化时程。最后对测试数据进行分类，最大分类正确率达到86．43％，通过最大分类正确率，最大信噪比，最大互信息等评价指标比较，验证了该方法的有效性，从而为大脑运动意识任务的特征提取及分类提供了新思路。     

事件相关电位在神经精神科的临床应用进展

事件相关电位(Event related potential，ERP)是认知神经科学领域中，评价大脑信息处理过程相关电活动的一种无创伤性检测手段。ERP作为大脑认知功能的客观检测技术，提供了一个观察脑内心理活动的直接窗口，已被用于视知觉、注意、记忆、语言等多领域的基础研究。由于ERP的高时间分辨率、对神经电信号的直接记录，使其能够进行即时检测及较准确地评价刺激处理过程中神经系统的损害，     

双人肢体协作动作运动想象脑电的ERD/ERS特征分析

目的 基于运动想象(motor imagery, MI)的脑机接口(brain computer interface, BCI)一般采用基于单人肢体动作的MI任务范式,诱发的事件相关去同步/同步(event-related desychronization/synchronization, ERD/ERS)模式及对应的可辨识思维类别数较为有限,无法满足BCI对外多指令控制。为此,本文在单人肢体动作MI的基础上引入双人肢体协作动作MI,探索双人肢体协作动作MI的脑电(electroencephalograph, EEG)信号的多脑区ERD/ERS特征。方法 采用自回归模型功率谱估计和事件相关谱扰动方法,对被试者执行单人左/右手动作MI、双人左/右手协作动作MI的EEG数据,进行频率-空间-时间特性对比分析与研究。结果 区别于单人左/右手动作MI,双人左/右手协作动作MI的EEG信号在大脑额叶区出现ERD特征,在感觉运动皮质区出现ERD、ERS特征,特征的频带更宽;感觉运动皮质区的ERD特征出现时间较晚、持续时间更长,且ERD、ERS特征的对比度更大。结论 在相同肢体部位的前提下,双人肢体...     

视觉听觉同时刺激模式下ERP的同步性研究

目的：研究视觉、听觉脑区在认知过程中的同步性。方法：设计了视觉、听觉同时刺激模式下的脑电实验，采用128道高密度脑电采集系统，记录了14位年龄在18～29岁之间的在校男性大学生的诱发脑电信号数据，并运用希尔伯特(Hilbert)相位同步算法对视觉、听觉区域的事件相关电位(ERP)进行同步量化。结果：在视听觉同时利用模式下，视觉脑区(枕叶)和听觉脑区(颞叶)之间的同步指数明显大于它们与其他脑区间的同步指数。结论：人在感知和认知事物时，相关的脑区间自动产生了神经活动的同步化。     

意识任务识别中事件相关脑电的时频域信息熵表达

事件相关脑电的量化表征对于研究意识任务识别和认识大脑思维机制具有重要意义.本研究对左右手想象意识任务的脑电信号进行小波包分析,提取出时频域信息熵用来表征事件相关脑电的变化;进而,分析了时频域信息熵特征的事件相关去同步/同步的变化时程,应用互信息评价时频域信息熵对事件相关脑电的表征能力,将相同步理论应用于导联间的脑电信号分析;设计时变线性分类器实现左右手想象运动意识任务识别,获得了满意的结果,最小分类错误率为9%.结果表明,时频域信息熵与频带能量具有一致的变化时程;时频域信息熵具有比频带能量更好的分离性,是事件相关去同步,同步的一个敏感的量化参数;时频域信息熵结合相同步相干性指数.能够提供更多反映大脑意识任务的状态信息.     

多类运动想象脑电信号的处理研究

基于运动想象的脑-机接口具有不依赖外界刺激器的特点,但如何根据不同受试者自适应地提取出最佳特征是目前的难点之一.本文设计了基于LabVIEW平台的运动想象脑电信号采集系统,对五名受试者想象左手、右手和脚运动时的脑电信号进行采集;利用小波包分解提取μ节律和β频段,实现脑电信号的滤波;通过分析不同受试者的小波包节点的ERD/ERS比率,自适应地选出最佳特征时间和频段;组合最佳特征时间、频段的小波包能量和小波包熵作为特征向量,利用马氏距离分类判别.实验结果证明:利用ERD/ERS比率、小波包分解和马氏距离分类,算法简单快捷,平均正确率可以达到84.3％,较好的实现了三类运动想象分类,提高了系统的自适应性.     

Event-related beta EEG changes during wrist movements induced by functional electrical stimulation of forearm muscles in man

Event-related beta electroencephalographic (EEG) changes were studied during wrist movements induced by functional electrical stimulation (FES) of the appropriate forearm muscles in healthy volunteers. Active and passive hand movements were investigated as control conditions. Significant EEG changes with respect to a pre-movement period were analyzed by calculating time-frequency maps of event-related (de-)synchronization (ERD/ERS) for 32 EEG channels recorded from sensorimotor and premotor areas. Immediately after the beginning of the FES movement, a prominent ERD was found, followed by a beta ERS similar to that observed after active or passive wrist movements. Both changes were maximal over the contralateral primary hand area. The main difference between active and stimulation-induced movements was that in the latter case no ERD was detectable prior to movement-onset. These findings suggest that the sensorimotor processing during FES involves some of the processes which are also involved in voluntary hand movements.     

Intracerebral recording of cortical activity related to self-paced voluntary movements: a Bereitschaftspotential and event-related desynchronization/synchronization. SEEG study

To analyze the distribution of the cortical electrical activity related to self-paced voluntary movements, i.e. the movement-related readiness potentials (Bereitschaftspotential, BP) and the event-related desynchronization (ERD) and synchronization (ERS) of cortical rhythms using intracerebral recordings. EEG was recorded in 14 epilepsy surgery candidates during preoperative video-stereo-EEG monitoring. Subjects performed self-paced hand movements, with their right and left fingers in succession. EEG signals were obtained from a total of 501 contacts using depth electrodes located in primary and nonprimary cortical regions. In accordance with previous studies, BP was found consistently in the primary motor (M1) and somatosensory (S1) cortex, the supplementary motor area (SMA), and in a few recordings also in the cingulate cortex and in the dorsolateral prefrontal and premotor cortex. ERD and ERS of alpha and beta rhythms were also observed in these cortical regions. The distribution of contacts showing ERD or ERS was larger than the distribution of those showing BP. In contrast to BP, ERD and ERS frequently occurred in the lateral and mesial temporal cortex and the inferior parietal lobule. The number of contacts and cortical regions showing ERD and ERS and not BP suggests that the two electrophysiological phenomena are differently involved in the preparation and execution of simple voluntary movements. Substantial differences between BP and ERD in spatial distribution and the widespread topography of ERD/ERS in temporal and higher-order motor regions suggest that oscillatory cortical changes are coupled with cognitive processes supporting movement tasks, such as memory, time interval estimation, and attention.     

Brain oscillatory 1-30 Hz EEG ERD/ERS responses during the different stages of an auditory memory search task

Event-related desynchronization (ERD) and event-related synchronization (ERS) responses of 1-30 Hz EEG frequencies during the different stages of an auditory Sternberg memory task were examined. The ERD/ERS responses were examined separately for successive memory set items (four) and for the two recognition conditions (YES/NO). The presentation of the memory set elicited ERS responses in the theta and alpha frequencies, and also beta ERD responses. These ERD/ERS responses elicited during encoding were found to evolve with successive memory set item presentation. The ERD/ERS responses elicited during the presentation of the probe dissociated significantly between the two recognition conditions (YES/NO). When the probe was included in the memory set (YES condition), recognition elicited stronger alpha and beta frequency ERD responses as compared to the NO condition. The findings from the current study verify that alpha ERD/ERS responses robustly dissociate between auditory encoding and recognition. The increasing alpha ERS responses with increasing memory set item presentation during encoding may be correlates of the functioning phonological loop, active memory maintenance and/or attention. The alpha ERD responses during recognition are undoubtedly associated with auditory memory search processes and distinguish between previously presented versus not presented verbal material. We propose that alpha ERD/ERS responses reflect explicitly auditory memory processes, discriminating between auditory encoding and recognition. Theta ERS responses may be associated with working memory processes, and possibly more specifically with the functioning of the central executive. Beta ERD/ERS responses may reflect also cognitive and/or memory processing, rather than merely the activity of the motor cortices.     

Event-related desynchronization/synchronization in the putamen. An SEEG case study

Event-related desynchronization (ERD) and synchronization (ERS) were studied during the invasive exploration of an epileptic surgery candidate. An electrode that was targeted in the amygdalo-hippocampal complex passed through the putamen with several contacts. During a simple self-paced motor task, we observed in the putamen a power decline (ERD) in both the alpha and beta frequency bands, and a rebound phenomenon (ERS) in the beta frequency band, concurrent with the movement of each hand. This is the first report of ERD/ERS in the basal ganglia. Electronic Publication     

Event-related dynamics of cortical rhythms: frequency-specific features and functional correlates.

Oscillations in the alpha and beta band (<35 Hz) display a dynamic behavior and show characteristic spatiotemporal patterns in sensory, motor and cognitive tasks. The event-related desynchronization (ERD) of alpha band and beta rhythms can be seen as a correlate of an activated cortical area with an increased excitability level of neurons. An event-related synchronization (ERS) of frequency components between 10 and 13 Hz may represent a deactivated cortical area or inhibited cortical network, at least under certain circumstances. It is hypothesized, that antagonistic ERD/ERS patterns, called 'focal ERD/surround ERS', may reflect a thalamo-cortical mechanism to enhance focal cortical activation by simultaneous inhibition of other cortical areas. Induced oscillations in the beta band (13-35 Hz, beta ERS) were found in sensorimotor areas after voluntary movement and after somatosensory stimulation. This may be interpreted as a state of 'inhibition' of neural circuitry in the primary motor cortex. Simultaneous activation of the motor cortex by e.g. motor imagery lead to an attenuation of the beta ERS. Moreover, there is evidence that the frequency of the induced beta oscillations represent a 'resonance-like frequency' of underlying cortical networks. However, further research is needed to investigate the functional meaning of bursts of beta oscillations below 35 Hz.     

基于脑电alpha波及运动想象的在线脑机接口系统设计

背景：目前在线脑机接口系统绝大多数采用同步式设计,无法区分“工作”状态与“空闲”状态。 目的：设计一种能够自由在“工作”与“空闲”状态间切换,方便灵活的脑机接口系统。 方法：设计了综合睁眼产生的alpha波阻断现象,以及进行运动想象时产生事件相关同步及去同步现象这些生理特征的在线脑机接口系统。通过检测使用者枕部脑电信号alpha波状况,来切换“空闲”与“工作”状态;在“工作”状态下,通过想象不同的肢体运动,分析运动皮质脑电信号的频率特征,来实现对外界的信息传输。 结果与结论：实验证明,经过训练的使用者在该在线脑机接口平台上可以自如的在不同状态间进行切换,并且能以很高的分类正确率发出控制命令。采用此方法进行设计,脑机接口系统的实用性得到了增强。     

EEG and fMRI Coregistration to Investigate the Cortical Oscillatory Activities During Finger Movement

Electroencephalography combined with functional magnetic resonance imaging (EEG-fMRI) may be used to identify blood oxygenation level dependent (BOLD) signal changes associated with physiological and pathological EEG event. In this study we used EEG-fMRI to determine the possible correlation between topographical movement-related EEG changes in brain oscillatory activity recorded from EEG electrodes over the scalp and fMRI-BOLD cortical responses in motor areas during finger movement. Thirty-two channels of EEG were recorded in 9 subjects during eyes-open condition inside a 1.5 T magnetic resonance (MR) scanner using a MR-compatible EEG recording system. Off-line MRI artifact subtraction software was applied to obtain continuous EEG data during␣fMRI acquisition. For EEG data analysis we used the event-related-synchronization/desynchronization (ERS/ERD) approach to investigate where movement-related decreases in alpha and beta power are located. For image statistical analysis we used a general linear model (GLM) approach. There was a significant correlation between the positive-negative ratio of BOLD signal peaks and ERD values in the electrodes over the region of activation. We conclude that combined EEG-fMRI may be used to investigate movement-related oscillations of the human brain inside an MRI scanner and the movement-related changes in the EMG or EEG signals are useful to identify the brain activation sources responsible for BOLD-signal changes.     

Computational model of thalamo-cortical networks: dynamical control of alpha rhythms in relation to focal attention.

EEG/MEG rhythmic activities such as alpha rhythms, of the visual or of the somato-sensory cortex, are commonly modulated as subjects perform certain tasks or react to specific stimuli. In general, these activities change depending on extrinsic or intrinsic events. A decrease of the amplitude of alpha rhythmic activity occurring after a given event, which manifests as a decrease of a spectral peak, is called event-related desynchronization (ERD), whereas the inverse is called event-related synchronization (ERS), since it is assumed that the power of a spectral peak is related to the degree of synchrony of the underlying oscillating neuronal populations. An intriguing observation in this respect [Pfurtscheller and Neuper, Neurosci. Lett. 174 (1994) 93-96] was that ERD of alpha rhythms recorded over the central areas was accompanied by ERS, within the same frequency band, recorded over neighboring areas. In case the event was a hand movement, ERD was recorded over the scalp overlying the hand cortical area, whereas ERS was concomitantly recorded over the midline, whereas if the movement was of the foot the opposite was found. We called this phenomenon 'focal ERD/surround ERS'. The question of how this phenomenon may be generated was approached by means of a computational model of thalamo-cortical networks, that incorporates basic properties of neurons and synaptic interactions. These simulation studies revealed that this antagonistic ERD/ERS phenomenon depends on the functional interaction between the populations of thalamo-cortical cells (TCR) and reticular nucleus cells (RE) and on how this interaction is modulated by cholinergic inputs. An essential feature of this interaction is the existence of cross-talk between different sectors of RE that correspond to distinct sensory modules (e.g. hand, foot). These observations led us to formulate the hypothesis that this basic neurophysiological mechanism can account for the general observation that enhanced attention given to a certain stimulus (the focus) is coupled to inhibition of attention to other stimuli (the surround).     

Event‐related EEG time‐frequency PCA and the orienting reflex to auditory stimuli

We recently reported an auditory habituation series with counterbalanced indifferent and significant (counting) instructions. Time‐frequency (t‐f) analysis of electrooculogram‐corrected EEG was used to explore event‐related synchronization (ERS)/desynchronization (ERD) in four EEG bands using arbitrarily selected time epochs and traditional frequency ranges. ERS in delta, theta, and alpha, and subsequent ERD in theta, alpha, and beta, showed substantial decrement over trials, yet effects of stimulus significance (count vs. no‐task) were minimal. Here, we used principal components analysis (PCA) of the t‐f data to investigate the natural frequency and time combinations involved in such stimulus processing. We identified four ERS and four ERD t‐f components: six showed decrement over trials, four showed count > no‐task effects, and six showed Significance × Trial interactions. This increased sensitivity argues for the wider use of our data‐driven t‐f PCA approach.