BACKGROUND & AIMS: :Magnetoencephalography (MEG) has become a standard approach to the investigation of human brain functions. This review starts with a brief review of the human visual system and studies on visual motion detection mechanisms is followed by the presentation of MEG studies that have contributed to the field. Emphasis is placed on the fact that because the neural activities measured in functional magnetic resonance imaging (fMRI) differ substantially from those measured in MEG--fMRI data cannot be used directly to estimate MEG signal sources. The basic ideas behind the methods of signal processing and analyses generally used in MEG studies are described and theoretical considerations of the neural mechanisms determining MEG response latency and amplitude changes are discussed. Here, scalar fields theory is proposed to explain MEG responses to incoherent motions, and the ways in which detection of complex motions such as transparency, rotation and expansion can be explained by this theory are also presented. Relationships between human behavioral reaction time and MEG response latency suggest a new concept underlying the reasons why humans are late in detecting slow motion.

背景与目标： : 脑磁图 (MEG) 已成为研究人脑功能的标准方法。本文从对人类视觉系统的简要回顾开始，然后对视觉运动检测机制进行研究，然后介绍对该领域做出贡献的MEG研究。强调的事实是，由于在功能磁共振成像 (fMRI) 中测得的神经活动与在MEG中测得的神经活动有很大不同-fMRI数据不能直接用于估计MEG信号源。描述了MEG研究中通常使用的信号处理和分析方法背后的基本思想，并讨论了确定MEG响应潜伏期和幅度变化的神经机制的理论考虑。在这里，提出了标量场理论来解释MEG对非相干运动的响应，并且还提出了可以通过该理论来解释诸如透明度，旋转和膨胀之类的复杂运动的检测方法。人类行为反应时间与MEG反应潜伏期之间的关系提出了一个新概念，这是人类迟于检测慢动作的原因。

BACKGROUND & AIMS: BACKGROUND:Following an ischemic stroke a highly variable clinical outcome is commonly evident despite similar onset symptoms as well as lesion characteristics. The aim of this study was to identify indexes providing early prediction of functional recovery, in addition to clinical severity and lesion dimension at onset of stroke. METHODS:In 32 patients, magnetoencephalographic (MEG) parameters collected in the acute phase (<10 days from symptoms onset, T0) from affected (AH) and unaffected (UH) hemispheres at rest and evoked by sensory stimuli were evaluated in association with the clinical outcome in a stabilized phase (T1, median 7.8 months) classified with three levels: worsening, partial and full recovery. RESULTS:Multiple multinomial logistic regression indicated AH gamma and UH delta band powers able to prognosticate clinical outcome at T1. After inclusion in this analysis, lesion volume had the strongest predictive ability, and UH delta band power remained as a predictive factor with a measurable cut-off, maximizing both sensitivity and specificity of the prediction: a patient with UH delta below cut-off would recover to some extent; a patient with UH delta above cut-off would have a probability of about 70% to worsen. CONCLUSIONS:MEG UH delta and AH gamma band powers were found to provide useful information about long-term outcome prognosis. Only the increase of delta band activity in the unaffected hemisphere contains information about the outcome in addition to the lesion volume.

背景与目标：

BACKGROUND & AIMS: :Magnetoencephalography offers the possibility of localizing accurately and noninvasively the source of intracranial currents associated with normal and abnormal brain activity. The purpose of this study was to assess the validity and across-subject reliability of localization of cortical sources responding to ipsilateral and contralateral auditory stimulation. Magnetic evoked fields to both stimulation conditions were measured in eight consecutive normal subjects, and the cortical sources of these fields were estimated on the basis of these measurements. Subsequent projection of the source location coordinates onto magnetic resonance images showed that in all subjects the sources were accurately estimated to fall in the vicinity of the auditory cortex and that two separate sources may account for the response to ipsilateral and contralateral stimulation.

背景与目标： : 脑磁图提供了准确，无创地定位与正常和异常大脑活动相关的颅内电流来源的可能性。这项研究的目的是评估响应同侧和对侧听觉刺激的皮质源定位的有效性和跨主题可靠性。在八个连续的正常受试者中测量了两种刺激条件下的磁诱发场，并根据这些测量结果估算了这些场的皮质源。随后将源位置坐标投影到磁共振图像上表明，在所有受试者中，可以准确地估计源落在听觉皮层附近，并且两个单独的源可能解释了对同侧和对侧刺激的反应。

BACKGROUND & AIMS: :Using magnetoencephalography, we investigated the spatiotemporal patterns of brain magnetic activity responsible for maintaining verbal and spatial information in either an integrated or an unintegrated fashion. Considering time dimension, we noted a greater activation of a fronto-parietal network in early latencies during the maintenance of integrated information, and a different pattern during the maintenance of unintegrated material, showing a greater activation in a fronto-posterior network in late latencies. The greater activation found in certain areas which are traditionally reported as being engaged in spatial working memory (i.e. superior frontal gyri, dorsolateral prefrontal cortex, superior and inferior parietal lobes) when subjects maintained integrated information could be explained by a greater weight of the spatial dimension. It is as if words somehow acquired a spatial attribute, thus exerting a greater load in a neural network specialized in spatial working memory. Alternatively, and not mutually exclusive, we also propose that during the maintenance of integrated information the allocation of cognitive resources is less interfering than during the maintenance of unintegrated information, making it easier.

背景与目标： : 使用脑磁图，我们研究了负责以集成或未集成方式维护言语和空间信息的大脑磁活动的时空模式。考虑到时间维度，我们注意到在维护集成信息的早期延迟中额顶网络的激活更大，而在维护未集成材料的过程中，额顶网络的激活更大，在后期延迟中额顶网络的激活更大。当受试者保持综合信息时，在传统上被报道为从事空间工作记忆的某些区域 (即上额叶回，背外侧前额叶皮层，上顶叶和下顶叶) 中发现的更大的激活可以通过更大的权重来解释空间维度。好像单词以某种方式获得了空间属性，从而在专门用于空间工作记忆的神经网络中施加了更大的负载。或者，并且不是相互排斥的，我们还建议在维护集成信息期间，认知资源的分配比维护未集成信息期间的干扰更少，从而使其更容易。

BACKGROUND & AIMS: OBJECTIVES:When using MEG for pre-surgical mapping it is critically important that reliable estimates of functional locations, such as the primary visual cortex (V1) can be provided. Several different models of MEG systems exist, each with varying software and hardware configurations, and it is not currently known how the system type contributes to variability in V1 localization. PATIENTS AND METHODS:In this study, participants underwent MEG sessions using two different systems (Vector View and CTF) during which they were presented with a repeating grating stimulus to the lower-left visual quadrant to generate a visual evoked field (VEF). The location, amplitude and latency of the VEF source was compared between systems for each participant. RESULTS:No significant differences were found in latency and amplitude between systems, however, a significant bias in the latero-medial position of the localization was present. The median inter-system Euclidian distance between V1 localization across participants was 10.5 mm. CONCLUSIONS:Overall, our results indicate that mapping of V1 can be reliably reproduced within approximately one centimetre by different MEG systems. SIGNIFICANCE:This result provides knowledge of the useful limits on the reliability of localization which can be taken into consideration in clinical practice.

背景与目标：

BACKGROUND & AIMS: PURPOSE:2-[18F]Fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) and magnetoencephalography (MEG) may assist in identifying the epileptogenic zone in children with nonlesional localization-related epilepsy. The aim of this study was to evaluate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FDG-PET, MEG, FDG-PET + MEG, and FDG-PET/MEG in children with nonlesional localization-related epilepsy. METHODS:Twenty-six children with localization-related epilepsy and who had normal or subtle changes on magnetic resonance imaging (MRI) underwent FDG-PET and MEG. Twenty-two patients had surgical resection, and surgical outcome was assessed using Engel classification. In patients with Engel I seizure outcome, we assessed the sensitivity, specificity, PPV, and NPV of lobar localization of MEG, FDG-PET, FDG-PET + MEG, and FDG-PET/MEG. KEY FINDINGS:Sixteen (72.7%) of 22 had Engel I seizure outcome. MEG was concordant with surgical resection in 18 patients, 14 had Engel I, and four had Engel II-IV outcomes. MEG was nonlocalizing or nonconcordant in four patients; two patients had Engel I and two had Engel II-IV outcomes. FDG-PET was concordant with surgical resection in 14 patients; 9 had Engel I outcome, and 5 had Engel II-IV outcome. FDG-PET was nonlocalizing or nonconcordant in seven patients with Engel I, and one with Engel III outcome. The sensitivity, specificity, PPV, and NPV of MEG were 85.0%, 99.1%, 94.4%, and 97.3%, respectively. The sensitivity, specificity, PPV, and NPV of FDG-PET were 65.0%, 94.4%, 68.4%, and 93.6%, respectively. There was no significant difference between MEG and FDG-PET for concordance with surgical resection (χ(2)  = 2.794, p = 0.095). FDG-PET + MEG, defined as two tests concordant with surgical resection, had reduced sensitivity and NPV, but increased specificity and PPV (55.0%, 92.3%, 100%, and 100%, respectively) relative to individual tests. FDG-PET/MEG, defined as one or both test(s) concordant with surgical resection, had increased sensitivity and NPV but reduced specificity (95.0%, 99.0%, and 93.5%, respectively) relative to individual tests. SIGNIFICANCE:The two tests FDG-PET and MEG were complementary in the assessment of children with localization-related epilepsy, particularly when one test was nonlocalizing or nonconcordant.

背景与目标：

BACKGROUND & AIMS: :Multimodal image integration is the procedure that puts together imaging data from multiple sources into the same space by a computerized registration process. This procedure is relevant to patients with difficult-to-localize epilepsy undergoing presurgical evaluation, who typically have many tests performed, including MR imaging, PET, ictal single-photon emission computed tomography, magnetoencephalography (MEG), and intracranial electroencephalogram (EEG). This article describes the methodology of such integration, focusing on integration of MEG. Also discussed is the clinical value of integration of MEG, in terms of planning of intracranial EEG implantation, interpretation of intracranial EEG data, planning of final resection, and addressing surgical failures.

背景与目标： : 多模态图像集成是通过计算机注册过程将来自多个来源的成像数据组合到同一空间的过程。此程序与接受术前评估的难以定位的癫痫患者有关，这些患者通常进行许多测试，包括MR成像，PET，发作性单光子发射计算机断层扫描，脑磁图 (MEG) 和颅内脑电图 (EEG)。本文介绍了这种集成的方法，重点是MEG的集成。还讨论了MEG整合的临床价值，包括颅内脑电图植入的计划，颅内脑电图数据的解释，最终切除的计划以及解决手术失败的问题。

BACKGROUND & AIMS: :Diagnosis of mild traumatic brain injuries (TBIs) has been difficult because of the absence of obvious focal brain lesions, using conventional computed tomography (CT) or magnetic resonance imaging (MRI) scans, in a large percentage of TBIs. One useful measure that can characterize potential tissue and neural network damage objectively is Lempel-Ziv complexity (LZC) applied to magnetoencephalography (MEG) signals. LZC is a model-independent estimator of system complexity that estimates the number of different patterns in a sequence. We hypothesized that because of the potential network damage, TBIs would show a reduced level of complexity in regions that are impaired. We included 18 healthy controls and 18 military veterans with TBI in the study. Resting state MEG data were acquired, and the LZCs were analyzed across the whole brain. Our results indicated reduced complexity in multiple brain areas in TBI patients relative to the healthy controls. In addition, we detected several neuropsychological measures associated with motor responses, visual perception, and memory, correlated with LZC, which likely explains some of the cognitive deficits in TBI patients.

背景与目标： : 由于使用常规计算机断层扫描 (CT) 或磁共振成像 (MRI) 扫描在很大一部分TBIs中没有明显的局灶性脑部病变，因此难以诊断轻度创伤性脑损伤 (TBIs)。一种可以客观地表征潜在组织和神经网络损伤的有用措施是应用于脑磁图 (MEG) 信号的Lempel-Ziv复杂性 (LZC)。LZC是系统复杂性的模型独立估计器，用于估计序列中不同模式的数量。我们假设，由于潜在的网络损害，tbi将显示受损区域的复杂性水平降低。在这项研究中，我们包括了18名健康对照者和18名患有TBI的退伍军人。获取静息状态MEG数据，并对整个大脑的LZCs进行分析。我们的结果表明，相对于健康对照组，TBI患者的多个大脑区域的复杂性降低。此外，我们检测到与运动反应，视觉感知和记忆相关的几种神经心理学指标，与LZC相关，这可能解释了TBI患者的某些认知缺陷。

BACKGROUND & AIMS: :We studied neuromagnetic fields during passive finger movements in 11 normal subjects. Activation started 27 ms after the onset of movement and remained for about 100 ms. Four activation maxima occurred within this time range, PM1 at 27 ms, PM2 at 46 ms, PM3 at 85 ms, and PM4 at 125 ms. Not all components were distinguishable in every subject partly due to overlapping effects, but PM3 was present in all subjects. Magnetic source imaging (MSI) revealed dipolar sources within 1 cm of the central sulcus for all four components. The results suggest that studying the integrity of the sensorimotor system in patients regardless of their degree of motor impairment is feasible.

背景与目标： : 我们研究了11名正常受试者被动手指运动期间的神经磁场。激活在运动开始后27毫秒开始，并保持约100毫秒。在这个时间范围内发生了四个激活最大值，PM1在27毫秒，PM2在46毫秒，PM3在85毫秒，PM4在125毫秒。并非所有成分在每个受试者中都是可区分的，部分原因是由于重叠效应，但是PM3存在于所有受试者中。磁源成像 (MSI) 揭示了所有四个组分在中心沟1厘米内的偶极源。结果表明，研究患者的感觉运动系统的完整性，无论其运动障碍的程度如何都是可行的。

BACKGROUND & AIMS: PURPOSE:To examine the behavioral effects and neural activation patterns associated with implicit semantic processing influences on phonological judgments during reading in children and adults. METHOD:Whole-head magnetoencephalography (MEG) recordings were obtained from 2 groups, children (9-13 years) and adults, performing a homophone judgment task. The stimuli consisted of pairs of sequentially presented written words that were either homophones, synonym foils, or unrelated control words. RESULTS:The difference in the time taken to respond to synonym pairs relative to control pairs of stimuli, called the semantic interference effect (SIE), was, on average, 24 ms for adults and 86 ms for children. Source analysis of the MEG data using minimum-norm estimation (MNE) yielded less activation in the adults for the synonym condition compared with the control condition in right anterior temporal and inferior frontal cortex 300-500 ms after the onset of the 2nd word in a pair, suggestive of semantic priming as well as inhibition of the SIE. A similar priming effect was observed for the children in left-anterior temporal cortex. CONCLUSION:The observed group differences in the magnitude of the SIE and brain activation patterns may reflect developmental differences in the effects of semantic information on phonological decisions during word processing.

背景与目标：

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背景与目标： -2

BACKGROUND & AIMS: :Increased survival of extremely low birth weight infants has led to a need for new prognostic methods to predict possible future neurological impairment. We investigated the early development of the somatosensory system by recording the somatosensory evoked magnetic fields (SEFs) during natural sleep at fullterm age in 16 very prematurely born infants and 16 healthy newborns born at term. The purpose was to determine possible changes in the function of the somatosensory cortex in the prematurely born infants by comparing the latency, strength, location and morphology of the SEFs with those of healthy fullterm newborns. We recorded reliable SEFs in all patients and controls. The equivalent current dipole (ECD) strength of the first cortical response, M60, was significantly lower in the patients. Otherwise, the general morphology and latency of the SEFs were similar in the two groups of babies. The similar response latencies in the two groups indicate normally developed conduction in the somatosensory system of the prematurely born infants. The attenuated ECD strength may reflect weaker synchrony in firing or a smaller number of the cortical neurons activated by the somatosensory stimulation. At the individual level, in four of the preterm infants, a later M200 response was not present or could not be modeled: all of them had lesions of the underlying hemisphere depicted by ultrasound and magnetic resonance imaging.

背景与目标： : 极低出生体重婴儿的存活率增加，导致需要新的预后方法来预测未来可能的神经系统损害。我们通过记录16个非常早产的婴儿和16个足月出生的健康新生儿在足月自然睡眠期间的体感诱发磁场 (SEFs)，研究了体感系统的早期发育。目的是通过比较sef与健康的足月新生儿的潜伏期，强度，位置和形态，确定早产婴儿体感皮层功能的可能变化。我们在所有患者和对照组中记录了可靠的SEFs。患者的第一皮质反应M60的等效电流偶极子 (ECD) 强度显着降低。否则，两组婴儿的SEFs的一般形态和潜伏期相似。两组的反应潜伏期相似，表明早产婴儿的体感系统传导正常。减弱的ECD强度可能反映了较弱的放电同步性或由体感刺激激活的较少数量的皮质神经元。在个体水平上，在四个早产儿中，后来的M200反应不存在或无法建模: 所有这些婴儿都具有超声和磁共振成像所描绘的潜在半球病变。

BACKGROUND & AIMS: :Identifying brain regions with high differential response under multiple experimental conditions is a fundamental goal of functional imaging. In many studies, regions of interest (ROIs) are not determined a priori but are instead discovered from the data, a process that requires care because of the great potential for false discovery. An additional challenge is that magnetoencephalography/electroencephalography sensor signals are very noisy, and brain source images are usually produced by averaging sensor signals across trials. As a consequence, for a given subject, there is only one source data vector for each condition, making it impossible to apply testing methods such as analysis of variance. We solve these problems in several steps. (1) To obtain within-condition uncertainty, we apply the bootstrap across trials, producing many bootstrap source images. To discover 'hot spots' in space and time that could become ROIs, (2) we find source locations where likelihood ratio statistics take unusually large values. We are not interested in isolated brain locations where a test statistic might happen to be large. Instead, (3) we apply a clustering algorithm to identify sources that are contiguous in space and time where the test statistic takes an 'excursion' above some threshold. Having identified possible spatiotemporal ROIs, (4) we evaluate global statistical significance of ROIs by using a permutation test. After these steps, we check performance via simulation, and then illustrate their application in a magnetoencephalography study of four-direction center-out wrist movement, showing that this approach identifies statistically significant spatiotemporal ROIs in the motor and visual cortices of individual subjects.

背景与目标： : 识别在多种实验条件下具有高差异反应的大脑区域是功能成像的基本目标。在许多研究中，感兴趣区域 (roi) 不是先验确定的，而是从数据中发现的，由于错误发现的巨大潜力，这一过程需要谨慎。另一个挑战是，脑磁图/脑电图传感器信号非常嘈杂，并且通常通过在试验中平均传感器信号来产生脑源图像。结果，对于给定的主题，每种条件只有一个源数据向量，因此无法应用诸如方差分析之类的测试方法。我们分几个步骤解决这些问题。(1) 为了获得条件内的不确定性，我们在试验中应用了引导程序，产生了许多引导程序源图像。为了发现可能成为roi的空间和时间中的 “热点”，(2) 我们找到了似然比统计值异常大的源位置。我们对测试统计数据可能很大的孤立大脑位置不感兴趣。相反，(3) 我们应用聚类算法来识别在空间和时间上连续的源，其中测试统计量的 “偏移” 超过某个阈值。在确定了可能的时空roi之后，(4) 我们通过使用置换检验评估roi的全局统计意义。在这些步骤之后，我们通过模拟检查性能，然后说明它们在四方向中心外手腕运动的脑磁图研究中的应用，表明这种方法可以识别单个受试者的运动和视觉皮质中具有统计意义的时空roi。

BACKGROUND & AIMS: :Magnetoencephalography (MEG) is used in clinical and fundamental studies of brain functions, primarily for the excellent temporal resolution it provides. The spatial resolution is often assumed to be poor, because of the ill-posed nature of MEG source modeling. However, the question of spatial resolution in MEG has seldom been studied in quantitative detail. Here we use the well-known retinotopic organization of the primary visual cortex (V1) as a benchmark for estimating the spatial resolution of MEG source imaging. Using a standard visual stimulation paradigm in human subjects, we find that individual MEG sources exhibit well-delineated visual receptive fields that collectively follow the known mapping of the retinal surface onto the cortex. Based on the size of these receptive fields and the variability of the signal, we are able to resolve MEG signals separated by approximately 7 mm in smooth regions of cortex and less than 1 mm for signals near curved gyri. The maximum resolution is thus comparable to that of the spacing of hypercolumns in human visual cortex. Overall, our results suggest that the spatial resolution of MEG can approach or in some cases exceed that of fMRI.

背景与目标： : 脑磁图 (MEG) 用于脑功能的临床和基础研究，主要用于其提供的出色的时间分辨率。由于MEG源建模的不适定性质，通常认为空间分辨率较差。但是，很少对MEG中的空间分辨率问题进行定量研究。在这里，我们使用初级视觉皮层 (V1) 的众所周知的视网膜组织作为估计MEG源成像空间分辨率的基准。在人类受试者中使用标准的视觉刺激范例，我们发现单个MEG源表现出轮廓分明的视觉感受野，这些视觉感受野共同遵循视网膜表面在皮层上的已知映射。基于这些感受野的大小和信号的可变性，我们能够解决MEG信号，该信号在皮层的光滑区域中被大约7毫米分开，而对于弯曲回旋附近的信号则小于1毫米。因此，最大分辨率与人类视觉皮层中超列的间距相当。总体而言，我们的结果表明，MEG的空间分辨率可以接近或在某些情况下超过fMRI。

BACKGROUND & AIMS: We have developed high-critical-temperature radio-frequency Super conducting QUantum Interference Devices (SQUIDs) with step-edge grain-boundary Josephson junctions and large flux focusers. These planar devices were fabricated from epitaxial YBa2Cu3O7 films and operated in the magnetometer and first-order gradiometer configurations while immersed in liquid nitrogen. At the temperature of 77K, we have attained a magnetic field resolution for the magnetometer better than 200 fT/Hz1/2 down to less than 1 Hz, i.e., over the low signal frequency range important for medical diagnostics. The results to date show a high promise for biomagnetic diagnostics. For the first time, we recorded the evoked responses from human brains using a high-temperature magnetometer and a first-order electronic gradiometer channel simultaneously. These results were obtained in a magnetically shielded room. An improvement in the magnetic field resolution by another order of magnitude is possible and probable.

背景与目标： 我们已经开发了具有阶跃边缘晶界约瑟夫森结和大通量聚焦器的高临界温度射频超导量子干涉器件 (squid)。这些平面器件是由外延YBa2Cu3O7薄膜制成的，并在磁力计和一阶梯度仪配置下工作，同时浸入液氮中。在77K的温度下，我们已经获得了比200 fT/Hz1/2低至小于1Hz的磁力计的磁场分辨率，即在对医学诊断重要的低信号频率范围内。迄今为止的结果表明，生物磁诊断具有很高的前景。我们首次同时使用高温磁力计和一阶电子梯度计通道记录了人脑的诱发反应。这些结果是在磁屏蔽室中获得的。磁场分辨率可能会提高另一个数量级。