Seizure-Onset Mapping Based on Time-Variant Multivariate Functional Connectivity Analysis of High-Dimensional Intracranial EEG: A Kalman Filter Approach

The visual interpretation of intracranial EEG (iEEG) is the standard method used in complex epilepsy surgery cases to map the regions of seizure onset targeted for resection. Still, visual iEEG analysis is labor-intensive and biased due to interpreter dependency. Multivariate parametric functional connectivity measures using adaptive autoregressive (AR) modeling of the iEEG signals based on the Kalman filter algorithm have been used successfully to localize the electrographic seizure onsets. Due to their high computational cost, these methods have been applied to a limited number of iEEG time-series (<60). The aim of this study was to test two Kalman filter implementations, a well-known multivariate adaptive AR model (Arnold et al. 1998) and a simplified, computationally efficient derivation of it, for their potential application to connectivity analysis of high-dimensional (up to 192 channels) iEEG data. When used on simulated seizures together with a multivariate connectivity estimator, the partial directed coherence, the two AR models were compared for their ability to reconstitute the designed seizure signal connections from noisy data. Next, focal seizures from iEEG recordings (73–113 channels) in three patients rendered seizure-free after surgery were mapped with the outdegree, a graph-theory index of outward directed connectivity. Simulation results indicated high levels of mapping accuracy for the two models in the presence of low-to-moderate noise cross-correlation. Accordingly, both AR models correctly mapped the real seizure onset to the resection volume. This study supports the possibility of conducting fully data-driven multivariate connectivity estimations on high-dimensional iEEG datasets using the Kalman filter approach.     

电极位置对振幅整合脑电图的影响

振幅整合脑电图(aEEG)是一种简化的脑功能监护手段,特别适合于新生儿脑功能监护,而测量电极的安放位置是aEEG方法推广过程中需要研究的一个关键问题.本研究通过对比分析不同脑电导联的aEEG结果,探讨电极分布位置及电极间距对aEEG波形的影响.结果显示,顶区及中央区附近是aEEG电极放置的较理想位置;aEEG波形的下边界对电极间距较敏感.     

Influence of Skull Modeling Approaches on EEG Source Localization

Electroencephalographic source localization (ESL) relies on an accurate model representing the human head for the computation of the forward solution. In this head model, the skull is of utmost importance due to its complex geometry and low conductivity compared to the other tissues inside the head. We investigated the influence of using different skull modeling approaches on ESL. These approaches, consisting in skull conductivity and geometry modeling simplifications, make use of X-ray computed tomography (CT) and magnetic resonance (MR) images to generate seven different head models. A head model with an accurately segmented skull from CT images, including spongy and compact bone compartments as well as some air-filled cavities, was used as the reference model. EEG simulations were performed for a configuration of 32 and 128 electrodes, and for both noiseless and noisy data. The results show that skull geometry simplifications have a larger effect on ESL than those of the conductivity modeling. This suggests that accurate skull modeling is important in order to achieve reliable results for ESL that are useful in a clinical environment. We recommend the following guidelines to be taken into account for skull modeling in the generation of subject-specific head models: (i) If CT images are available, i.e., if the geometry of the skull and its different tissue types can be accurately segmented, the conductivity should be modeled as isotropic heterogeneous. The spongy bone might be segmented as an erosion of the compact bone; (ii) when only MR images are available, the skull base should be represented as accurately as possible and the conductivity can be modeled as isotropic heterogeneous, segmenting the spongy bone directly from the MR image; (iii) a large number of EEG electrodes should be used to obtain high spatial sampling, which reduces the localization errors at realistic noise levels.     

鼻腔内机械振荡刺激对健康人群静息态脑电图相对功率及有效连接的影响

鼻腔内机械振荡刺激(iMVS)是一种新型的无创神经刺激技术,可提升边缘系统内在功能活性从而改善自主神经平衡.通过分析iMVS对健康人群脑电图(EEG)相对功率以及EEG有效连接的影响,探索iMVS的神经生理机制.将22名健康成年被试随机均分为刺激组与对照组,并对11名刺激组被试两侧鼻腔各进行10 min的iMVS,11...     

基于PCA多导联的癫痫脑电信号分类及致痫灶定位研究

为了更好的对致痫灶进行准确定位,提出了一种基于PCA(主成分分析)的定位方法.针对非线性动力学方法从不同角度提取癫痫脑电信号特征,首先采用主成分分析对高维特征向量进行降维处理,用随机森林进行分类;随后利用医学参考值范围找出各导联的差异变化,进而实现对致痫灶的初步定位.     

Influence of measurement noise and electrode mislocalisation on EEG dipole-source localisation

Measurement noise in the electro-encephalogram (EEG) and inaccurate formation about the locations of the EEG electrodes on the head induce localisation errors in the results of EEG dipole source analysis. These errors are studied by performing dipole source localisation for simulated electrode potentials in a spherical head model, for a range of different dipole locations and for two different numbers (27 and 148) of electrodes. Dipole source localisation is performed by iteratively minimising the residual energy (RE), using the simplex algorithm. The ratio of the dipole localisation error (cm) to the noise level (%) of Gaussian measurement noise amounts to 0.15 cm/% and 0.047 cm/% for the 27 and 148 electrode configurations, respectively, for a radial dipole with 40% eccentricity The localisation error due to noise can be reduced by taking into account multiple time instants of the measured potentials. In the case of random displacements of the EEG electrodes, the ratio of dipole localisation errors to electrode location errors amounts to 0.78 cm⁻¹ cm and 0.27 cm⁻¹ cm for the 27 and 148 electrode configurations, respectively. It is concluded that it is important to reduce the measurement noise, and particularly the electrode mislocalisation, as the influence of the latter is not reduced by taking into account multiple time instants.     

Influence of Parent Artery Segmentation and Boundary Conditions on Hemodynamic Characteristics of Intracranial Aneurysms

Purpose

The purpose of this study is to explore the influence of segmentation of the upstream and downstream parent artery and hemodynamic boundary conditions (BCs) on the evaluated hemodynamic factors for the computational fluid dynamics (CFD) analysis of intracranial aneurysms.

Materials and Methods

Three dimensional patient-specific aneurysm models were analyzed by applying various combinations of inlet and outlet BCs. Hemodynamic factors such as velocity pattern, streamline, wall shear stress, and oscillatory shear index at the systolic time were visualized and compared among the different cases.

Results

Hemodynamic factors were significantly affected by the inlet BCs while there was little influence of the outlet BCs. When the inlet length was relatively short, different inlet BCs showed different hemodynamic factors and the calculated hemodynamic factors were also dependent on the inlet length. However, when the inlet length (L) was long enough (L>20D, where D is the diameter of inlet section), the hemodynamic factors became similar regardless of the inlet BCs and lengths. The error due to different inlet BCs was negligible. The effect of the outlet length on the hemodynamic factors was similar to that of the inlet length.

Conclusion

Simulated hemodynamic factors are highly sensitive to inlet BCs and upstream parent artery segmentation. The results of this work can provide an insight into how to build models and to apply BCs for more accurate estimation of hemodynamic factors from CFD simulations of intracranial aneurysms.     

Source Localization of P300 from Oddball, Single Stimulus, and Omitted-Stimulus Paradigms

Three different auditory stimulus paradigms were used to elicit P300 potentials. Normal subjects were tested on the classical rare target stimulus, single-stimulus and omitted-stimulus conditions. Noninvasive identification of the cerebral sources of the event-related potentials (ERPs) was performed using spatio-temporal multiple dipole modeling (BESA software) with individually sized spherical head models. The grand average data of each condition was first independently modeled and these models were used as starting values for modeling each individual subject's data. Models for the rare-stimulus condition and single-stimulus condition both consisted of 6 dipoles. Models for the omitted-stimulus condition consisted of 2 dipoles. The dipole locations of the final individual 6-dipole models for the rare and single-stimulus conditions did not differ significantly from each other or from one previous result obtained from a another group of subjects (Tarkka et al. 1995). Super-imposition of the dipole coordinates on the sterotaxic brain atlas suggests that bilateral deep medial temporal lobe structures are the major contributors to rare and single-stimulus P300s. Because both the wave form morphology and the source model of the P300 elicited by single stimulus were close to those of the rare-stimulus P300 it may be that the underlying neural mechanisms eliciting these P300 potentials are essentially the same.     

基于脑电信号溯源分析的音乐类型对学习记忆影响的研究

音乐在日常生活中充当着重要的角色,它对学习认知活动的影响受到越来越多学者的重视。在无音乐、古典音乐、摇滚音乐等3种背景音乐下,对20名被试记忆单词的脑电实验,采用sLORETA溯源方法对脑电数据进行分析,并采用统计非参数映射方法(SnPM)对3种溯源结果进行两两对比分析。结果发现,不同音乐类型下的事件相关电位(ERP)源主要分布在额叶和颞叶。其中,无音乐状态下P300溯源结果主要分布在额叶和左侧大脑的颞叶部分,古典音乐和摇滚音乐状态下P300溯源结果主要分布在额叶和右侧大脑的颞叶部分。对溯源结果进行统计分析,发现不同音乐类型下的ERP源电流密度两两之间均有显著性差异(P<0.05),其中:无音乐和古典音乐两种情形相比,差异主要集中在颞叶;无音乐和摇滚音乐两种情形相比,差异主要集中在颞叶和额叶;古典音乐和摇滚音乐两种情形相比,差异主要集中在额叶和部分枕叶。对行为学数据进行统计分析发现,无音乐状态下被试记忆单词的正确率均值约为91.00%±0.64%,古典音乐状态下约为86.00%±0.45%,摇滚音乐状态下约为80.00%±0.24%。研究结果表明,音乐对大脑产生的刺激,可能会减少大脑用于当前认知加工过程时的资源,降低学习记忆的效率。     

The Influence of Musical Training on Patterns of EEG Asymmetry During Musical and Non-Musical Self-Generation Tasks

Musically proficient and non-proficient right-handed subjects were requested to list in a pre-experimental questionnaire three familiar songs, whose words and melody were well known. They were then instructed in two separate experiments, to whistle the melody of a song, talk the lyrics to a song, or sing a song each for 3 1-min trials performed with eyes closed. EEG was recorded from the left and right occipital areas (O₁ and O₂) in Experiment I and from the left and right parietal areas (P₃ and P₄) in Experiment II, and filtered for 8–13 Hz activity on-line. Comparable results were obtained in both experiments and indicated that non-musically trained subjects show significantly greater relative right hemisphere activation while whistling the melody of a song vs talking the lyrics to a song. Musically trained subjects show no differences in EEG asymmetry between these tasks. In addition, there were no group differences in asymmetry during the talking and singing conditions. These data are consistent with recent evidence suggesting that musical training is associated with the adoption of an analytic and sequential processing mode toward melodic information, and suggest that long term training in complex cognitive skills has functional neural concomitants.     

Dissociating Effects of Number of Phonemes, Number of Syllables, and Syllabic Complexity on Word Production in Aphasia: It's the Number of Phonemes that Counts

Many people with aphasia show effects of word length on the accuracy of their word production. However, it is unclear from previous research whether this is an effect of number of phonemes, number of syllables or the complexity of the syllable structure (number of consonant clusters), as these factors are usually confounded. This paper is the first to attempt to dissociate the effects of these three factors on word production in a case series of nine English-speaking aphasic individuals. Using carefully controlled stimuli and analysis using logistic regression, the effects of these highly intercorrelated variables can be distinguished. Significant effects of number of phonemes were found on word production accuracy in English but there was no evidence for independent effects of number of syllables, number of clusters (syllabic complexity), or syllable frequency (once the intercorrelations between these variables had been controlled). It is argued that these data are consistent with any theory of spoken word production that incorporates a level of processing where phonemes are represented and that level is a potential source of error.     

Influence of Competing Distractors on Response Selection in Huntington's Disease and Parkinson's Disease

Current theories of the basal ganglia suggest a functional role in filtering stimuli that are competing for response selection. We hypothesised that damage to the basal ganglia, as occurs in Huntington's disease (HD) and Parkinson's disease (PD), may alter the effects of distractors on this filtering process. Fourteen HD subjects, 16 PD subjects, and age-matched healthy controls performed an ignored repetition test of negative priming. Negative priming was defined as a significant time cost in responding to a target that shared features with the distractor from the previous trial. Results indicated that whereas healthy controls and PD subjects showed normal negative priming, HD subjects failed to show negative priming. The results indicate that disruption to cells in the neostriatum, but not necessarily to cells in the substantia nigra, may affect selective attention by altering the influence of distractor stimuli competing for action.     

Influence of Competing Distractors on Response Selection in Huntington's Disease and Parkinson's Disease

Current theories of the basal ganglia suggest a functional role in filtering stimuli that are competing for response selection. We hypothesised that damage to the basal ganglia, as occurs in Huntington's disease (HD) and Parkinson's disease (PD), may alter the effects of distractors on this filtering process. Fourteen HD subjects, 16 PD subjects, and age-matched healthy controls performed an ignored repetition test of negative priming. Negative priming was defined as a significant time cost in responding to a target that shared features with the distractor from the previous trial. Results indicated that whereas healthy controls and PD subjects showed normal negative priming, HD subjects failed to show negative priming. The results indicate that disruption to cells in the neostriatum, but not necessarily to cells in the substantia nigra, may affect selective attention by altering the influence of distractor stimuli competing for action.     

The Influence of Age and Breeding Conditions on the Number and Proliferation of Intraepithelial Lymphocytes in Pigs

The number and subset composition of intraepithelial lymphocytes (IEL) were studied in pigs in different age groups ranging from 1 day to 4.5 years. There were no major differences between the numbers of IEL in the jejunum and ileum. The postnatal increase of IEL largely depended on the breeding conditions: in germ-free animals there was a constant level, while in conventionally bred pigs the numbers increased more obviously than in specified pathogen-free (SPF) pigs. As the numbers of IEL can rise due to increased influx from other organs, decreased emigration, decreased apoptosis or local proliferation, the incorporation of the DNA precursor bromodeoxyuridine (BrdU) by IEL was studied after different labelling protocols. There were low but definite numbers of BrdU+ IEL 1 h after BrdU, indicating in-situ proliferation in conventional animals with a tendency to a higher index in the jejunum than the ileum. Repetitive labelling protocols for 14 days resulted in 12-20% BrdU+ IEL, which may be caused by local proliferation and immigration of lymphocytes produced in other lymphoid organs as documented for the pig. Future studies need to focus on the factors regulating local proliferation and the migration of IEL in different species.     

高血压各期的EEG、EBAM、TCD、CT的研究

对９４例高血压病各期患者的ＥＥＧ，ＢＥＡＭ、ＴＣＤ观察，并与ＣＴ进行对比发现：高血压病不仅是单纯的内科疾病，在发病的早期就已经引起了脑功能和脑血流动力学的改变，这些改变以及变化的程度均可以通过ＥＥＧ，ＢＥＡＭ和ＴＣＤ等脑功能性检查手段来测定。高血压各期ＥＥＧ、ＢＥＡＭ、ＴＣＤ均有不同的特点，随着病情的改变而改变。这些手段均不能被ＣＴ等形态学的检查方法所代替。这些指标对于诊治高血压病，预报和防治脑血管病的发生具有重要的价值。     

Influence of lateralized neuropsychological activities with and without sensorimotor components on EEG spectral power (alpha-rhythm).

Spectral analysis of the EEG (alpha-rhythm) was studied in 8 young right-handed men who underwent 6 experimental tasks which were compared with rest, and included two pure motor activities using only the right and then the left hand, two pure neuropsychological tasks, and two "mixed" tasks with both neurophysiological and motor activities. The electrophysiological parameters studied were the log of spectral power and an asymmetry index (RP-LP)/(RP + LP). In order to demonstrate lateralization of the EEG, one must associate lateralized motor and neuropsychological tasks (which are supposed to preferentially involve one of the cerebral hemispheres). These results may reconcile apparently divergent views published in the literature with respect to lateralized EEG modifications associated with cognitive activities.