Spike‐associated networks and intracranial electrographic findings

Aims. Functional connectivity is providing new insights into the network nature of epilepsy with growing clinical applications. Our objective was to validate a novel magnetoencephalography‐based method to non‐invasively measure the epileptic network. Methods. We retrospectively identified pediatric and adult patients with refractory focal epilepsy who underwent pre‐surgical magnetoencephalography with subsequent intracranial electrographic monitoring. Magnetoencephalography tracings were visually reviewed, and interictal epileptiform discharges (“spikes”) were individually marked. We then evaluated differences in whole‐brain connectivity during brief epochs preceding the spikes and during the spikes using the Network‐Based Statistic to test differences at the network level. Results. In six patients with statistically‐significant network differences, we observed substantial overlap between the spike‐associated networks and electrographically active areas identified during intracranial monitoring (the spike‐associated network was 78% and 83% sensitive for intracranial electroencephalography‐defined regions in the irritative and seizure onset zones, respectively). Conclusion. These findings support the neurobiological validity of the spike‐associated network method. Assessment of spike‐associated networks has the potential to improve surgical planning in epilepsy surgery patients by identifying components of the epileptic network prior to implantation.     

Functional Organization of the Human First and Second Somatosensory Cortices: a Neuromagnetic Study

Multichannel neuromagnetic recordings were used to differentiate signals from the human first (SI) and second (SII) somatosensory cortices and to define representations of body surface in them. The responses from contralateral SI, peaking at 20 – 40 ms, arose mainly from area 3b, where representations of the leg, hand, fingers, lips and tongue agreed with earlier animal studies and with neurosurgical stimulations and recordings on convexial cortex in man. Representations of the five fingers were limited to a cortical strip of ∼2 cm in length. Responses from SII peaked 100 – 140 ms after contra- and ipsilateral stimuli and varied considerably from one subject to another. Signs of somatotopical organization were seen also in SII. Responses of SII were not fully recovered at interstimulus intervals of 8 s.     

A Neuromagnetic Study of the Functional Organization of the Sensorimotor Cortex

Movement-related neuromagnetic fields from eight healthy human subjects were investigated in a Bereitschaftspotential paradigm. The three conditions studied were right-sided mouth, index finger and foot movement. The neuromagnetic field patterns corresponding to the motor field and the movement-evoked field I were analysed using a moving dipole model. For both components a somatotopic organization was found: the estimated dipole locations for the mouth were more lateral and those for the foot more medial than the estimated dipole positions for the index finger movement. With regard to possible clinical applications, e.g. non-invasive mapping of the sensorimotor cortex and studies of plasticity of the motor function, the present results suggest that the investigation of movement-evoked field I for the index finger condition is most likely to yield further results.     

Auditory event-related magnetic fields in a tone-duration discrimination task. Source localization for the mismatch field and for a new component M2"

Auditory event related magnetic fields were measured using an odd-ball paradigm in which the rare event was a tone of short duration, D2, and the frequent one a tone of longer duration, D1. The subjects were required to attend to and count the number of rare stimuli. In the average across target stimuli a mismatch field (MMF) occurs and the dependence of the MMF, especially its latency, on the tone duration D2 is examined in detail. The location of an equivalent current dipole for the MMF-source is found and turns out to be at variance with earlier results. In addition to the MMF we propose a new component, here called MMF, which in time overlaps the magnetic equivalent of the P200 signal and which has a source location (equivalent current dipole) lying rather close to the MMF-source. The two sources are, however, active at latencies differing by a time equal to D2. We speculate that MMF indicates the onset of the process: "evaluation of tone-duration" while the MMF indicates the end of this process.     

脑磁图在癫痫灶定位中的应用

目的：应用脑磁图（MEG）对癫痫灶进行定位，探讨脑磁图对癫痫灶定位的价值。方法：应用美国4D Vectorview306通道全头型生物磁仪，对21例癫痫患（其中男13例，女8例，年龄3－52岁，平均23．7岁）进行发作间期脑磁图检查。结果：17例测得发作间期棘波，4例未检测到棘波，结论：脑磁图对癫痫灶定位有很高的应用价值。     

母语为汉语者听觉性语言中枢的定位

目的采用脑磁图(magnetoencephalography,MEG)的等价偶极子定位法(equivalent current dipole,ECD)和合成孔径磁场定位法(synthetic aperture magnetometry,SAM)定位母语为汉语健康自愿者的听觉性语言中枢,探讨汉字的语言加工过程。方法对15例母语为汉语的健康受试者采用北京大学附属第一医院制定的利手评定标准进行利手评定,采用给予听动物名称、植物名称的语言任务刺激,用MEG记录刺激后产生的诱发磁场,将采集的数据与MRI叠加,定位听觉性语言中枢。结果所有受试者听到动物名称、植物名称后均在双侧大脑半球诱发出明显的晚发磁反应波,其中左侧大脑半球磁反应波分化较右侧大脑半球好。结论母语为汉语的正常人听觉性语言中枢与经典的语言中枢基本相符,即听觉性语言中枢定位于左侧颞中回、颞上回、缘上回。