A novel method for extracting interictal epileptiform discharges in multi-channel MEG: Use of fractional type of blind source separation

ObjectiveVisual inspection of interictal epileptiform discharges (IEDs) in multi-channel MEG requires a time-consuming evaluation process and often leads to inconsistent results due to variability of IED waveforms. Here, we propose a novel extraction method for IEDs using a T/k type of blind source separation (BSS_T/k).MethodsWe applied BSS_T/k with seven patients with focal epilepsy to test the accuracy of identification of IEDs. We conducted comparisons of the results of BSS components with those obtained by visual inspection in sensor-space analysis.ResultsBSS_T/k provided better signal estimation of IEDs compared with sensor-space analysis. Importantly, BSS_T/k was able to uncover IEDs that could not be detected by visual inspection. Furthermore, IED components were clearly extracted while preserving spike and wave morphology. Variable IED waveforms were decomposed into one dominant component.ConclusionsBSS_T/k was able to visualize the spreading signals over multiple channels into a single component from a single epileptogenic zone. BSS_T/k can be applied to focal epilepsy with a simple parameter setting.SignificanceOur novel method was able to highlight IEDs with increased accuracy for identification of IEDs from multi-channel MEG data.     

Altered effective connectivity network in patients with insular epilepsy: A high-frequency oscillations magnetoencephalography study

ObjectiveThe project aimed to determine the alterations in the effective connectivity (EC) neural network in patients with insular epilepsy based on interictal high-frequency oscillations (HFOs) from magnetoencephalography (MEG) data.MethodsWe studied MEG data from 22 insular epilepsy patients and 20 normal subjects. Alterations in spatial pattern and connection properties of the patients with insular epilepsy were investigated in the entire brain network and insula-based network.ResultsAnalyses of the parameters of graph theory revealed the over-connectivity and small-world configuration of the global connectivity patterns observed in the patients. In the insula-based network, the insular cortex ipsilateral to the seizure onset displayed increased efferent and afferent EC. Left insular epilepsy featured strong connectivity with the bilateral hemispheres, whereas right insular epilepsy featured increased connectivity with only the ipsilateral hemisphere.ConclusionsPatients with insular epilepsy display alterations in the EC network in terms of both whole-brain connectivity and the insula-based network during interictal HFOs.SignificanceAlterations of interictal HFO-based networks provide evidence that epilepsy networks, instead of epileptic foci, play a key role in the complex pathophysiological mechanisms of insular epilepsy. The dysfunction of HFO networks may prove to be a novel promising biomarker and the cause of interictal brain dysfunctions in insular epilepsy.     

EEG和MEG在额叶癫痫致痫灶定位的价值

目的：评估脑电图（EEG）和脑磁图（MEG）在难治性额叶癫痫（FLE）致痫灶定位的价值,以提高术前定位的准确性。方法：16例FLE患者,根据临床发作表现、发作间期和发作期EEG、MRI、PET—CT的检查结果进行综合评估后致痫灶定位仍困难,再行MEG检查。其中9例行手术治疗,术中皮层脑电图（ECoG）和／或深部电极脑电图（DEEG）监测并验证术前定位的准确性。结果：本组发作表现、EEG、MRI、PET—CT能准确定位的比率分别为：18．75％、31．25％、25％、43．75％;MEG棘波源定位优于EEG,可局限在脑回水平;EEG记录的痫性波范围比MEG广,但棘波优势区与MEG结果一致;术中ECoG和／或DEEG监测结果证实MEG定位的准确性。结论：MEG是一种能准确定位FLE致痫灶的术前无创性检查技术,与EEG检查相结合,可全面反映FLE的电生理状态,为外科手术治疗提供帮助。     

Multi-modal investigation of transcranial ultrasound-induced neuroplasticity of the human motor cortex

IntroductionThere is currently a gap in accessibility to neuromodulation tools that can approximate the efficacy and spatial resolution of invasive methods. Low intensity transcranial focused ultrasound stimulation (TUS) is an emerging technology for non-invasive brain stimulation (NIBS) that can penetrate cortical and deep brain structures with more focal stimulation compared to existing NIBS modalities. Theta burst TUS (tbTUS, TUS delivered in a theta burst pattern) is a novel repetitive TUS protocol that can induce durable changes in motor cortex excitability, thereby holding promise as a novel neuromodulation tool with durable effects.ObjectiveThe aim of the present study was to elucidate the neurophysiologic effects of tbTUS motor cortical excitability, as well on local and global neural oscillations and network connectivity.MethodsAn 80-s train of active or sham tbTUS was delivered to the left motor cortex in 15 healthy subjects. Motor cortical excitability was investigated through transcranial magnetic stimulation (TMS)-elicited motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) using paired-pulse TMS. Magnetoencephalography (MEG) recordings during resting state and an index finger abduction-adduction task were used to assess oscillatory brain responses and network connectivity. The correlations between the changes in neural oscillations and motor cortical excitability were also evaluated.ResultstbTUS to the motor cortex results in a sustained increase in MEP amplitude and decreased SICI, but no change in ICF. MEG spectral power analysis revealed TUS-mediated desynchronization in alpha and beta spectral power. Significant changes in alpha power were detected within the supplementary motor cortex (Right > Left) and changes in beta power within bilateral supplementary motor cortices, right basal ganglia and parietal regions. Coherence analysis revealed increased local connectivity in motor areas. MEP and SICI changes correlated with both local and inter-regional coherence.ConclusionThe findings from this study provide novel insights into the neurophysiologic basis of TUS-mediated neuroplasticity and point to the involvement of regions within the motor network in mediating this sustained response. Future studies may further characterize the durability of TUS-mediated neuroplasticity and its clinical applications as a neuromodulation strategy for neurological and psychiatric disorders.     

Where left becomes right: a magnetoencephalographic study of sensorimotor transformation for antisaccades

To perform a saccadic response to a visual stimulus, a 'sensorimotor transformation' is required (i.e., transforming stimulus location into a motor command). Where in the brain is this accomplished? While previous monkey neurophysiology and human fMRI studies examined either parietal cortex or frontal eye field, we studied both of these regions simultaneously using magnetoencephalography (MEG). Nineteen healthy participants performed a pseudorandom series of prosaccades and antisaccades during MEG. Antisaccades require a saccade in the direction opposite a suddenly appearing stimulus. We exploited this dissociation between stimulus and saccadic direction to identify cortical regions that show early activity for a contralateral stimulus and late activity for a contralateral saccade. We found that in the left hemisphere both the intraparietal sulcus and the frontal eye field showed a pattern of activity consistent with sensorimotor transformation - a transition from activity reflecting the direction of the stimulus to that representing the saccadic goal. These findings suggest that sensorimotor transformation is the product of coordinated activity across the intraparietal sulcus and frontal eye field, key components of a cortical network for saccadic generation.     

脑磁图及弥散张量成像在中央区低级别胶质瘤手术中的应用

目的 探讨联合利用脑磁图(MEG)、弥散张量成像技术(DTI)和神经导航技术,在中央区低级别胶质瘤切除中神经功能保护的作用.方法 对40例涉及中央区的Ⅱ级脑胶质瘤患者,随机分成对照组和试验组两组,每组20例.对照组按照常规神经导航定位肿瘤行手术切除;试验组将脑磁图、DTI与神经导航序列影像融合进行术中导航,术中可视下定位脑皮质功能区及皮质下传导束,来实现精确切除病灶.术后3d内行MRI、DTI检查,比较两组患者的肿瘤切除程度、神经传导束完整性及术后1个月神经功能恢复情况、KPS评分.结果 试验组肿瘤全切除率85％ (17/20)显著高于对照组55％ (11/20);试验组术后致瘫率25％ (5/20)显著低于对照组60％(12/20);试验组术后1个月平均KPS评分(84.50±21.6)分显著高于对照组(64.05±33.36)分.两组在肿瘤切除率、纤维束(FA值)、神经功能保存、KPS评分上的比较,差异均具有统计学意义(均P＜0.05).结论 通过联合利用MEG、DTI及神经导航技术,可最大限度地切除中央区胶质瘤,并更好地保留患者的神经功能,提高其生存质量.     

A demonstration that task difficulty can confound the interpretation of lateral differences in brain activation between typical and dyslexic readers

Dyslexic readers (DRs) manifest atypical patterns of brain activity, which may be attributed to aberrant neural connectivity and/or an attempt to activate compensatory pathways. This paper evaluates whether differences in brain activation patterns between DRs and typical readers (TRs) are confounded by task difficulty. Eight DRs and eight TRs matched for age, sex, and nonverbal IQ performed pseudoword rhyming tasks at two levels of difficulty during magnetoencephalography. Task difficulty varied with the number of successive target pseudowords presented before the test pseudoword. Regions of interest were: the temporoparietal area (TPA), the ventral occipital temporal area (VOT), and the inferior frontal gyrus (IFG). Activity was analysed for the 660-ms period after test pseudoword onset. During the discrepant performance condition left hemispheric TPA activation increased across time for TRs, but not DRs, and IFG bihemispheric activation was greater in TRs by the end of the trial. During the equivalent performance condition no group differences in TPA or IFG activation were found. We argue that these results indicate that direct comparison of DR versus TR brain activity is confounded when DRs are more challenged than TRs. This highlights the importance of equating reading group performance during neuroimaging of reading-related tasks.     

Magnetic source imaging and ictal SPECT in MRI‐negative neocortical epilepsies: Additional value and comparison with intracranial EEG

Purpose: To investigate the utility of magnetic source imaging (MSI) and ictal single photon emission computed tomography (SPECT), each compared with intracranial electroencephalography (EEG) (ICEEG), to localize the epileptogenic zone (EZ) and predict epilepsy surgery outcome in patients with nonlesional neocortical focal epilepsy. Methods: Studied were 14 consecutive patients with nonlesional neocortical epilepsy who underwent presurgical evaluation including ICEEG, positive MSI, and localizing subtraction Ictal SPECT coregistered to MRI (SISCOM) analysis. Follow‐up after epilepsy surgery was ≥24 months. ICEEG, MSI, and SPECT results were classified using a sublobar classification. Key Findings: Of 14 patients, 6 (42.9%) became seizure‐free after surgery. Sublobar ICEEG focus was completely resected in 11 patients; 5 (45.5%) of them became seizure‐ free. Concordance of ICEEG and MSI and complete focus resection was found in 5 (35.7%) patients; 80% of them became seizure‐free. Sublobar ICEEG‐MSI concordance and complete focus resection significantly increased the chance of seizure freedom after epilepsy surgery (p = 0.038). In contrast, of the 6 patients (42.9%) with concordant ICEEG and SISCOM and complete focus resection, only 66.7% became seizure‐free (p = 0.138). Assuming concordant results, the additive value to ICEEG alone for localizing the EZ is higher with ICEEG‐MSI (odds ratio 14) compared to ICEEG‐SISCOM (odds ratio 6). Significance: This study shows that combination of MSI and/or SISCOM with ICEEG is useful in the presurgical evaluation of patients with nonlesional neocortical epilepsy. Concordant test results of either MSI or SISCOM with ICEEG provide useful additive information for that provided by ICEEG alone to localize the EZ in this most challenging group of patients. When sublobar concordance with ICEEG is observed, MSI is more advantageous compared to SISCOM in predicting seizure‐free epilepsy surgery outcome.     

Magnetoencephalography to confirm epileptiform discharges mimicking small sharp spikes in temporal lobe epilepsy

ObjectiveTo determine whether magnetoencephalography (MEG) can identify epileptiform discharges mimicking small sharp spikes (SSSs) on scalp electroencephalography (EEG) in patients with temporal lobe epilepsy (TLE).MethodsWe retrospectively reviewed simultaneous scalp EEG and MEG recordings of 83 consecutive patients with TLE and 49 with extra-TLE (ETLE).ResultsSSSs in scalp EEG were detected in 15 (18.1%) of 83 TLE patients compared to only two (4.1%) of 49 ETLE patients (p = 0.029). Five of the 15 TLE patients had MEG spikes with concurrent SSSs in EEG, but neither of the 2 ETLE patients. Three of these 5 TLE patients had additional interictal epileptiform discharges (IEDs) in EEG and MEG. Equivalent current dipoles (ECDs) of MEG spikes with concurrent SSSs and IEDs showed no difference in temporal lobe localization and horizontal orientation, whereas ECD moments were smaller in MEG spikes with concurrent SSSs than those with IEDs.ConclusionsSSSs were more common in TLE than in ETLE. At least some morphologically diagnosed SSSs are true but low-amplitude epileptiform discharges in TLE which can be identified with simultaneous MEG.SignificanceSimultaneous MEG is useful to identify epileptiform discharges mimicking SSSs in patients with TLE.