Magnetoencephalography in pediatric lesional epilepsy surgery

This study was performed to assess the usefulness of magnetoencephalography (MEG) as a presurgical evaluation modality in Korean pediatric patients with lesional localization-related epilepsy. The medical records and MEG findings of 13 pediatric patients (6 boys and 7 girls) with localization-related epilepsy, who underwent epilepsy surgery at Seoul National University Children's Hospital, were retrospectively reviewed. The hemispheric concordance rate was 100% (13/13 patients). The lobar or regional concordance rate was 77% (10/13 patients). In most cases, the MEG spike sources were clustered in the proximity of the lesion, either at one side of the margin (nine patients) or around the lesion (one patient); clustered spike sources were distant from the lesion in one patient. Among the patients with clustered spike sources near the lesion, further extensions (three patients) and distal scatters (three patients) were also observed. MEG spike sources were well lateralized and localized even in two patients without focal epileptiform discharges in the interictal scalp electroencephalography. Ten patients (77%) achieved Engel class I postsurgical seizure outcome. It is suggested that MEG is a safe and useful presurgical evaluation modality in pediatric patients with lesion localization-related epilepsy.     

Spatiotemporal frequency characteristics of cerebral oscillations during the perception of fundamental frequency contour changes in one-syllable intonation

Accurate perception of fundamental frequency (F0) contour changes in the human voice is important for understanding a speaker's intonation, and consequently also his/her attitude. In this study, we investigated the neural processes involved in the perception of F0 contour changes in the Japanese one-syllable interjection “ne” in 21 native-Japanese listeners. A passive oddball paradigm was applied in which “ne” with a high falling F0 contour, used when urging a reaction from the listener, was randomly presented as a rare deviant among a frequent “ne” syllable with a flat F0 contour (i.e., meaningless intonation). We applied an adaptive spatial filtering method to the neuromagnetic time course recorded by whole-head magnetoencephalography (MEG) and estimated the spatiotemporal frequency dynamics of event-related cerebral oscillatory changes in the oddball paradigm. Our results demonstrated a significant elevation of beta band event-related desynchronization (ERD) in the right temporal and frontal areas, in time windows from 100 to 300 and from 300 to 500 ms after the onset of deviant stimuli (high falling F0 contour). This is the first study to reveal detailed spatiotemporal frequency characteristics of cerebral oscillations during the perception of intonational (not lexical) F0 contour changes in the human voice. The results further confirmed that the right hemisphere is associated with perception of intonational F0 contour information in the human voice, especially in early time windows.     

A comparison of stimulus synchronous activity in the primary motor cortices of athletes and non-athletes

In this study, we measured primary motor cortex (MI) activity during a reaction time task to examine the appearance of MI activity that synchronized with the stimulus presentation (stimulus synchronous MI activity, SSMA). Because brain activity was expected to be enhanced by the repetitive/extensive activation, we hypothesized that the SSMA would be more clearly observable in athletes who were trained to perform reactive movements than in non-athletes. MI activity was measured in ten athletes and ten non-athletes by magnetoencephalography. The tasks were a simple reaction task and a Go/Nogo reaction task in which the subjects were asked to abduct their right index fingers in response to a visual stimulus. The Go/Nogo reaction time task was adopted to confirm the presence of the SSMA, because the MI activity in response to a Nogo stimulus did not overlap with the MI activity that was synchronous with the execution of the movement. The results show that the SSMA was clearly apparent in the athlete group (9/10). In the non-athlete group, however, only three subjects showed the SSMA (3/10). Moreover, the MI activity of the athletes tended to be larger than that of the non-athletes, even though the athletes did not specifically practice these index finger movements during their daily training. We concluded that long-term physical training promotes MI activity and the effects of reactive task repetition were more clearly apparent in the MI activity of the athletes.     

Post-movement beta rebound abnormality as indicator of mirror neuron system dysfunction in autistic spectrum disorder: An MEG study

The mu rhythm is regarded as a physiological indicator of the human mirror neuron system (MNS). The dysfunctional MNS hypothesis in patients with autistic spectrum disorder (ASD) has often been tested using EEG and MEG, targeting mu rhythm suppression during action observation/execution, although with controversial results. We explored neural activity related to the MNS in patients with ASD, focusing on power increase in the beta frequency band after observation and execution of movements, known as post-movement beta rebound (PMBR). Multiple source beamformer (MSBF) and BrainVoyager QX were used for MEG source imaging and statistical group analysis, respectively. Seven patients with ASD and ten normal subjects participated in this study. During the MEG recordings, the subjects were asked to observe and later execute object-related hand actions performed by an experimenter. We found that both groups exhibited pronounced PMBR exceeding 20% when observing and executing actions with a similar topographic distribution of maximal activity. However, significantly reduced PMBR was found only during the observation condition in the patients relative to controls in cortical regions within the MNS, namely the sensorimotor area, premotor cortex and superior temporal gyrus. Reduced PMBR during the observation condition was also found in the medial prefrontal cortex. These results support the notion of a dysfunctional execution/observation matching system related to MNS impairment in patients with ASD, and the feasibility of using MEG to detect neural activity, in particular PMBR abnormalities, as an index of MNS dysfunction during performance of motor or cognitive tasks.     

Cortico-cortical phase synchrony in auditory mismatch processing

Previous studies have shown a reduced MMN in patients with lesions in the temporal or frontal lobes, suggesting a temporal-frontal involvement in change detection. However, how the temporal lobe interacts with other brain areas in responding to unexpected deviant stimuli remains unclear. This study aimed to evaluate the functional connectivity between cerebral regions by measuring the phase synchrony of magnetoencephalographic (MEG) signals elicited by regular simple tones and their duration-deviants in an oddball paradigm. We measured MEG responses to deviant (1000-Hz frequency, 50-ms duration, probability of 15%) and standard (1000-Hz frequency, 100-ms duration) sounds in 10 healthy adults. By using the Morlet wavelet-based analysis, relative phase synchronization values of 4-40 Hz MEG responses at 150-300 ms after stimulus onset were calculated with respect to a reference channel from the temporal region. Phase synchronization was clearly identified between the temporal and ipsilateral frontal region in the auditory evoked responses. This temporal-frontal synchronization was significantly larger in deviants-elicited than standards-elicited activation at 4-25 Hz in the left hemisphere (p < 0.05), and at 4-8 Hz in the right hemisphere (p < 0.01). Also, temporal-temporal and temporal-parietal phase synchronies were found in deviants-evoked 4-8 Hz responses.The present results suggest an involvement of temporal-temporal, temporal-frontal, and temporal-parietal neuronal network in detecting auditory change. Phase synchronization analysis may provide a useful window to further understanding of the cerebral reactivity during the processing of auditory deviants.     

Auditory evoked fields to illusory sound source movements

Auditory motion can be simulated by presenting binaural sounds with time-varying interaural intensity differences. We studied the human cortical response to both the direction and the rate of illusory motion by recording the auditory evoked magnetic fields with a 122-channel whole-head neuromagnetometer. The illusion of motion from left to right, right to left, and towards and away from the subject was produced by varying a 6-dB intensity difference between the two ears in the middle of a 600-ms tone. Both the onset and the intensity transition within the stimulus elicited clear responses in auditory cortices of both hemispheres, with the strongest responses occurring about 100 ms after the stimulus and transition onsets. The transition responses were significantly earlier and larger for fast than slow shifts and larger in the hemisphere contralateral to the increase in stimulus intensity for azimuthal shifts. Transition response amplitude varied with the direction of the simulated motion, suggesting that these responses are mediated by directionally selective cells in auditory cortex.     

Superior temporal gyrus spectral abnormalities in schizophrenia

Considerable evidence indicates early auditory stimulus processing abnormalities in schizophrenia, but the mechanisms are unclear. The present study examined oscillatory phenomena during a paired-click paradigm in the superior temporal gyrus (STG) as a possible core problem. The primary question addressed is whether first click and/or second click group differences in the time-domain evoked response in patients with schizophrenia are due to (1) group differences in the magnitude of poststimulus oscillatory activity, (2) group differences in poststimulus phase-locking, and/or (3) group differences in the magnitude of ongoing background oscillatory activity. Dense-array magnetoencephalography from 45 controls and 45 patients with schizophrenia produced left- and right-hemisphere STG 50- and 100-ms time-frequency evoked, phase-locking, and total power measures. Whereas first click 100-ms evoked theta and alpha abnormalities were observed bilaterally, evoked low beta-band differences were specific to the left hemisphere. Compared to controls, patients with schizophrenia showed more low-frequency phase variability, and the decreased 100-ms S1 evoked response observed in patients was best predicted by the STG phase-locking measure.     

Localization of Broca's area using verb generation tasks in the MEG: Validation against fMRI

Functional MRI (fMRI) is routinely used to non-invasively localize language areas. Magnetoencephalography (MEG) is being explored as an alternative technique. MEG tasks to localize receptive language are well established although there are no standardized tasks to localize expressive language areas. We developed two expressive language tasks for MEG and validated their localizations against fMRI data. Ten right-handed adolescents (μ = 17.5 years) were tested with fMRI and MEG on two tasks: verb generation to pictures and verb generation to words. MEG and fMRI data were normalized and overlaid. The number of overlapping voxels activated in fMRI and MEG were counted for each subject, for each task, at different thresholding levels. For picture verb generation, there was 100% concordance between MEG and fMRI lateralization, and for word verb generation, there was 75% concordance. A count showed 79.6% overlap of voxels activated by both MEG and fMRI for picture verb generation and 50.2% overlap for word verb generation. The percentage overlap decreased with increasingly stringent activation thresholds. Our novel MEG expressive language tasks successfully identified neural regions involved in language production and showed high concordance with fMRI laterality. Percentage overlap of activated voxels was also high when validated against fMRI, but showed task-specific and threshold-related effects. The high concordance and high percentage overlap between fMRI and MEG activations confirm the validity of our new MEG task. Furthermore, the higher concordance from the picture verb generation task suggests that this is a promising task for use in the young clinical population.     

基于PCA和LDA数据降维的脑磁图脑机接口研究

脑磁图(MEG)信号作为一种新的脑-机接口(BCI)输入信号,含有手运动方向的模式信息。通常对MEG信号采用信号处理的特征提取和线性分类,识别率一直难于提高。本文提出用主成分分析(PCA)方法对其进行特征提取,并用线性判别分析(LDA)进行了优化,最后用最近邻非线性分类器进行分类,在分类结果的基础上分析了混淆矩阵。实验结果表明PCA+LDA方法能有效的分析多通道的MEG信号,平均识别率达到了53.0%,优于BCI竞赛Ⅳ的识别率46.9%。     

急性枕叶脑梗死患者视觉皮质中枢脑磁图变化特征

目的研究急性枕叶脑梗死患者视觉皮层中枢脑磁图(MEG)的变化特征。方法对6例急性单侧枕叶梗死表现为对侧视野同向偏盲患者于发病后2周内行视觉诱发磁场(VEFs)测试,并检测8名健康志愿者作为正常对照。刺激选取黑白棋盘格翻转图形。分别记录两组受试者VEFs的M100波峰产生的潜伏期、波形、等电流偶极(ECD)强度和磁源性影像(MSI)。结果所有受试者VEFs反应的最基本波形为M100,位于距状裂两侧的皮质。与正常对照组相比,患者健侧枕叶的VEFs反应波形,潜伏期和ECD强度并无明显差异(均P>0.05),而患侧枕叶的VEF反应则出现了波形异常,潜伏期明显延长和ECD强度显著降低(均P<0.05)异常,且MSI显示其M100反应的ECD位置分布紊乱。结论MEG可检测出急性枕叶脑梗死患者视觉皮质中枢功能的损伤,并能够客观的评价患者视觉皮层中枢的功能状态。