Magnetoencephalographic and electrocorticographic studies on the epileptogenic focus in a patient with Kojewnikow syndrome

Partial motor seizures occur, followed after a variable interval by well-localized myoclonic jerks, in the patients with Kojewnikow syndrome, or epilepsia partialis continua. However, the epileptogenic focus remains to be established. We studied the epileptogenic focus of a 17-year-old boy with intractable Kojewnikow syndrome. Interictal EEG, ictal EEG, jerk-locked averaging, and ictal SPECT revealed a left central focus. A giant SEP indicated increased exitability of the primary sensory area. Magnetoencephalogram (MEG) and electrocorticogram identified the epileptogenic focus in the pre- and post-central cortex, indicating involvement of both the primary motor and sensory areas. Surgical treatment was successful. Thus, MEG proved to be the most accurate tool in the presurgical evaluation.     

Ictal MEG in two children with partial seizures

We report on the successful identification of epileptic foci in two children with partial epilepsy using ictal magnetoencephalography (MEG). Case 1 is a 12-year-old male suffering with simple partial seizures with leftwards nystagmus. Ictal SPECT revealed a hyperperfusion area in the right lateral occipital area, and MRI revealed cortical dysplasia in the same area. Interictal EEG dipoles were concentrated in the right mesial occipital lobe. Both interictal and ictal MEG dipoles were concentrated in the right mesial occipital lobe, which corresponded well with neuroimaging data and his clinical features. Case 2 is a 5-year-old female suffering with simple partial seizures with left-side facial twitching. Interictal EEG dipoles were located in her left motor area, the pre-sylvian fissure, close to the location of the interictal MEG-estimated dipoles. Ictal EEGs showed no remarkable changes associated with her clinical manifestations. However, ictal MEG showed high-voltage slow waves over her left hemisphere, and ictal MEG iso-contour maps revealed a clear dipolar pattern, which suggested that the MEG dipole was located in the area of the sylvian fissure. Ictal SPECT revealed hyperperfusion areas around the left sylvian fissure. Conclusion: Ictal MEG is useful for determining the precise location of epileptic focus in patients with motionless seizures, including children.     

Investigation of the normal proximal somatomotor system using magnetoencephalography.

OBJECTIVE: The role of the ipsilateral cortex in proximal muscle control in normal human subjects is still under debate. One clinical finding, rapid recovery of proximal muscle relative to distal muscle use following stroke, has led to the suggestion that the ipsilateral as well as the contralateral motor cortex may be involved in normal proximal muscle control. The primary goal of this project was to identify contralateral and ipsilateral motor cortex activation associated with proximal muscle movement in normal subjects using magnetoencephalography (MEG). METHODS: We developed protocols for a self-paced bicep motor task and a deltoid, electrical-stimulation somatosensory task. The MEG data were analyzed using automated multi-dipole spatiotemporal modeling techniques to localize the sources and characterize the associated timing of these sources. RESULTS: Reliable contralateral primary motor and somatosensory sources localized to areas consistent with the homunculus. Ipsilateral M1 activation was only found in 2/12 hemispheres. CONCLUSIONS: Robust contralateral motor cortex activation and sparse ipsilateral motor cortex activation suggest that the ipsilateral motor cortex is not involved in normal proximal muscle control. SIGNIFICANCE: The results suggest that proximal and distal muscle control is similar in normal subjects in the sense that proximal muscle control is primarily governed by the contralateral motor cortex.     

Magnetoencephalographic localization in pediatric epilepsy surgery: comparison with invasive intracranial electroencephalography.

The object of this study was to determine the concordance of the anatomical location of interictal magnetoencephalographic (MEG) spike foci with the location of ictal onset zones identified by invasive ictal intracranial electroencephalographic recordings in children undergoing evaluation for epilepsy surgery. MEG was performed in 11 children with intractable, nonlesional, extratemporal, localization-related epilepsy. Subsequently, chronic invasive intracranial electroencephalographic monitoring was performed by using subdural electrodes to localize the ictal onset zone and eloquent cortex. Based on the invasive monitoring data, all children had excision of, or multiple subpial transections through, ictal onset cortex and surrounding irritative zones. In 10 of 11 patients, the anatomical location of the epileptiform discharges as determined by MEG corresponded to the ictal onset zone established by ictal intracranial recordings. In all children, the anatomical location of the somatosensory hand area, determined by functional mapping through the subdural electrode array, was the same as that delineated by MEG. Nine of 11 patients became either seizure-free or had a greater than 90% reduction in seizures after surgery, with a mean follow-up of 24 months. MEG is a powerful and accurate tool in the presurgical evaluation of children with refractory nonlesional extratemporal epilepsy.     

Interictal and ictal magnetoencephalographic study in patients with medial frontal lobe epilepsy

PURPOSE: To determine whether magnetoencephalography (MEG) has any clinical value for the analysis of seizure discharges in patients with medial frontal lobe epilepsy (FLE). METHODS: Four patients were studied with 74-channel MEG. Interictal and ictal electroencephalographic (EEG) and MEG recordings were obtained. The equivalent current dipoles (ECDs) of the MEG spikes were calculated. RESULTS: In two patients with postural seizures, interictal EEG spikes occurred at Cz or Fz. The ECDs of interictal MEG spikes were localized around the supplementary motor area. In the other two patients with focal motor or oculomotor seizures, interictal EEG spikes occurred at Fz or Cz. The ECDs of interictal MEG spikes were localized at the top of the medial frontal region. The ECDs detected at MEG ictal onset were also localized in the same area as those of the interictal discharges. CONCLUSIONS: In medial FLE patients, interictal and ictal MEG indicated consistent ECD localization that corresponded to the semiology of clinical seizures. Our findings demonstrate that MEG is a useful tool for detecting epileptogenic focus.     

Magneto-encephalographic correlates of the lateralized readiness potential.

To determine the onset of movement-related EEG activity accompanying stimulus-induced movements, it is commonly isolated from overlapping stimulus-related activity by a subtraction procedure, yielding the lateralized readiness potential (LRP). In order to elucidate the generation of the LRP and to explore whether magnetoencephalographic (MEG) measures have advantages over the LRP as a measure of response selection, MEG activity was recorded in four healthy adults during self-paced and stimulus-induced hand movements. Self-paced movements were preceded by readiness fields in all subjects, explained by sources in contralateral and (for 2/8 response sides) also ipsilateral hemispheres. Movement-related activity preceding stimulus-induced movements could only be modeled adequately when stimulus-related activity was removed by subtracting MEG signals for left and right hand movements. Thus identified source locations showed no systematic deviation from the sources for readiness fields, supporting a generation of the movement-related activity in primary motor cortex. The corresponding source waveforms allowed latency determinations of motor cortex activity as markers for response-choice timing. MEG thus provides information on the time course of hand-specific motor cortex activation for each hemisphere separately, where the electro-encephalographic LRP provides a composite measure for both hemispheres.     

Post-stroke tactile allodynia and its modulation by vestibular stimulation: a MEG case study

Background – There is behavioural evidence that caloric vestibular stimulation (CVS) can alleviate central pain. Several such patients have also noted that it reduces tactile allodynia, an especially ill‐understood phenomenon in these patients. Aims of the study – The first aim is to use magnetoencephalography (MEG) to study neural activity associated with tactile allodynia in central post‐stroke pain (CPSP). The second is to assess how this would be affected, if at all, by CVS. The third is to assess the ability of the VESTAL solution for MEG to detect anterior cingulate activation. Methods – A 58‐year‐old woman with CPSP, and marked unilateral tactile allodynia, participated in a MEG study with imaging pre‐ and post‐CVS. Results – Tactile simulation within the patient’s allodynic area resulted in contralateral activation of the primary motor and anterior cingulate cortices, which had normalized 24 h post‐CVS. Conclusions – We suggest that the unexpected primary motor cortex activation in response to light touch in the allodynic area arises from inappropriate activation of a normal mechanism, which may occur when a threat to homeostasis is present, to lower motor thresholds and allow for more rapid performance of corrective actions. We propose this may be mediated by the interoceptive cortex in the dorsal posterior insula.     

Ictal magnetoencephalography in temporal and extratemporal lobe epilepsy

PURPOSE: We evaluated visual patterns and source localization of ictal magnetoencephalography (MEG) in patients with intractable temporal lobe epilepsy (TLE) and extratemporal epilepsy (ETE). METHODS: We performed spike and seizure recording simultaneously with EEG and MEG on two patients with TLE and five patients with ETE. Scalp EEG was recorded from 21 channels (10-20 international system), whereas MEG was recorded from two 37-channel sensors. We compared ictal EEG and MEG onset, frequency, and evolution and performed MEG dipole source localization of interictal spikes and early ictal discharges and co-registered dipoles to brain magnetic resonance imaging (MRI). We correlated dipole characteristics with intracranial EEG, surgical resection, and outcome. RESULTS: Ictal MEG lateralized seizure onset in both TLE patients and demonstrated ictal onset, frequency, and evolution in accordance with EEG. Ictal MEG source analysis revealed tangential vertical dipoles in the anterolateral angle in one patient, and anterior dipoles with anteroposterior orientation in the other. Intracranial EEG revealed regional entorhinal seizure onset in the first patient. Both patients became seizure free after temporal lobectomy. In ETE, ictal MEG demonstrated visual patterns similar to ictal EEG and had concordant localization with interictal MEG in all five patients. Two patients underwent surgery. Ictal MEG localization was concordant with intracranial EEG in both cases. One patient had successful outcome after surgery. The second patient did not improve after limited resection and multiple subpial transections. CONCLUSIONS: Ictal MEG can demonstrate ictal onset frequency and evolution and provide useful localizing information before epilepsy surgery.     

Detectability of cerebellar activity with magnetoencephalography and electroencephalography

Electrophysiological signals from the cerebellum have traditionally been viewed as inaccessible to magnetoencephalography (MEG) and electroencephalography (EEG). Here, we challenge this position by investigating the ability of MEG and EEG to detect cerebellar activity using a model that employs a high‐resolution tessellation of the cerebellar cortex. The tessellation was constructed from repetitive high‐field (9.4T) structural magnetic resonance imaging (MRI) of an ex vivo human cerebellum. A boundary‐element forward model was then used to simulate the M/EEG signals resulting from neural activity in the cerebellar cortex. Despite significant signal cancelation due to the highly convoluted cerebellar cortex, we found that the cerebellar signal was on average only 30–60% weaker than the cortical signal. We also made detailed M/EEG sensitivity maps and found that MEG and EEG have highly complementary sensitivity distributions over the cerebellar cortex. Based on previous fMRI studies combined with our M/EEG sensitivity maps, we discuss experimental paradigms that are likely to offer high M/EEG sensitivity to cerebellar activity. Taken together, these results show that cerebellar activity should be clearly detectable by current M/EEG systems with an appropriate experimental setup.     

Hemifacial motor and crying seizures of temporal lobe onset: case report and review of electro-clinical localisation

OBJECTIVE: To report a case of temporal lobe epilepsy with clinical presentation of paroxysmal episodes of "tightness" over the right hemiface, and ictal crying, and review electroclinical localisation of this phenomenon. METHODS: Clinical semiology, neurophysiological localising tests, and epilepsy surgery outcome are reported in a subject presenting with paroxysmal right hemifacial movements and ictal crying. Pertinent past reports of somato-motor signs and ictal crying in temporal lobe epilepsy are reviewed and the findings correlated with proposed human facial cortical representation. RESULTS: Simple partial seizures caused by temporal lobe epilepsy presented with right sided tonic facial movements and ictal crying. Intracranial EEG monitoring documented a left medial temporal onset of seizures that remained asymptomatic until they propagated to the left cingulate region. Anterior temporal lobectomy with resection of the amygdala and anterior hippocampus resulted in cessation of seizures. CONCLUSIONS: This is a rare example of epileptic seizures of medial temporal onset presenting with isolated somato-motor manifestations and ictal crying. Anatomical-electrical-clinical correlations with cortical regions controlling facial movements were highly suggestive that this case represents secondary activation of "emotional" motor cortex M3 and M4 (rostral and caudal cingulate motor cortex), giving rise to focal hemifacial movements and ictal crying.     

Ictal SPECT in supplementary motor area seizures

OBJECTIVES: We used ictal single photon emission computed tomography (SPECT) to clarify the propagation pathways of epileptic discharges in patients with supplementary motor area (SMA) seizure. METHODS: In four patients (four males, age range, 18-27 years) with SMA seizures, SPECT studies by radioisotope 99mTc-ECD were performed as a preoperative evaluation. Two of the patients remained seizure-free after complete resection of the focal cortical dysplasia on magnetic resonance (MR) images including epileptic foci. In the other two patients, MR images were normal, but subdural electrode monitoring allowed for verifying the ictal onset in the left SMA. After partial resection of the SMA including epileptic foci, these patients experienced a significant (>90%) reduction of seizure frequency. Regional cerebral blood flow (rCBF) measurements obtained under ictal and interictal conditions were compared on a voxel-by-voxel basis by means of the SPM99 paired t-test option (uncorrected p<0.001). RESULTS: Significant increases in rCBF under ictal conditions were identified in the bilateral anterior cingulate cortex (ACC), the globus pallidus ipsilateral to epileptic foci and the contralateral cerebellar hemisphere. The right ACC included a cluster with a submaximum in the right primary sensorimotor area. DISCUSSION: In patients with SMA seizures, the hyperperfusion areas of ictal SPECT did not localize within the SMA but spread to the adjacent cortex such as the ACC and sensorimotor cortex ipsilateral to epileptic foci. Additionally, the epileptic discharges propagated to the remote areas such as the globus pallidus and cerebellum. We caution that ictal SPECT localization in patients with SMA seizures is not always concordant to epileptic focus but reveals already spread seizure activities.     

Topographic movie of intracranial ictal high-frequency oscillations with seizure semiology: epileptic network in Jacksonian seizures

Purpose: We developed a technique to produce images of dynamic changes in ictal high‐frequency oscillations (HFOs) >40 Hz recorded on subdural electroencephalography (EEG) that are time‐locked to the ictal EEG and ictal semiology video. We applied this technique to Jacksonian seizures to demonstrate ictal HFO propagation along the homunculus in the primary sensory‐motor cortex to visualize the underlying epileptic network. Methods: We analyzed intracranial ictal EEGs from two patients with intractable Jacksonian seizures who underwent epilepsy surgery. We calculated the degrees of increase in amplitude within 40–80, 80–200, and 200–300 Hz frequency bands compared to the interictal period and converted them into topographic movies projected onto the brain surface picture. We combined these data with the ictal EEGs and video of the patient demonstrating ictal semiology. Key Findings: The ictal HFOs began in the sensory cortex and appeared concomitantly with the sensory aura. They then propagated to the motor cortex at the same time that focal motor symptoms evolved. As the seizure progressed, the ictal HFOs spread or reverberated in the rolandic region. However, even when the seizure became secondarily generalized, the ictal HFOs were confined to the rolandic region. In both cases, there was increased amplitude of higher frequency bands during seizure initiation compared to seizure progression. Significance: This combined movie showed the ictal HFO propagation corresponding to the ictal semiology in Jacksonian seizures and revealed the epileptic network involved in seizure initiation and progression. This method may advance understanding of neural network activities relating to clinical seizure generation and propagation.     

Ictal onset localization of epileptic seizures by magnetoencephalography

OBJECTIVES: The aim of this study was to localize the ictal onset zone of focal epileptic seizures by magnetoencephalography (MEG) and to compare the results with interictal MEG localizations, ictal and interictal electroencephalography (EEG) results and magnetic resonance imaging (MRI) in epilepsy surgery candidates. MATERIALS AND METHODS: Data of 13 patients with partial seizures during MEG recording were analysed. Measurements were performed with a Magnes II dual unit system. RESULTS: In six of 13 cases, the ictal onset zone could be localized by MEG, with all interictal MEG findings being confirmed by ictal MEG results. In four cases, the ictal MEG localization results were corresponding to the ictal EEG localization results. In two cases, EEG yielded no comparable information. CONCLUSION: Ictal onset localization is feasible with MEG. Both interical and ictal MEG contribute valuable information to the presurgical assessment of epilepsy patients.     

Activation of cortical and cerebellar motor areas during executed and imagined hand movements: an fMRI study.

Brain activation during executed (EM) and imagined movements (IM) of the right and left hand was studied in 10 healthy right-handed subjects using functional magnetic resonance imagining (fMRI). Low electromyographic (EMG) activity of the musculi flexor digitorum superficialis and high vividness of the imagined movements were trained prior to image acquisition. Regional cerebral activation was measured by fMRI during EM and IM and compared to resting conditions. Anatomically selected regions of interest (ROIs) were marked interactively over the entire brain. In each ROI activated pixels above a t value of 2.45 (p<0.01) were counted and analyzed. In all subjects the supplementary motor area (SMA), the premotor cortex (PMC), and the primary motor cortex (M1) showed significant activation during both EM and IM; the somatosensory cortex (S1) was significantly activated only during EM. Ipsilateral cerebellar activation was decreased during IM compared to EM. In the cerebellum, IM and EM differed in their foci of maximal activation: Highest ipsilateral activation of the cerebellum was observed in the anterior lobe (Larsell lobule H IV) during EM, whereas a lower maximum was found about 2-cm dorsolateral (Larsell lobule H VII) during IM. The prefrontal and parietal regions revealed no significant changes during both conditions. The results of cortical activity support the hypothesis that motor imagery and motor performance possess similar neural substrates. The differential activation in the cerebellum during EM and IM is in accordance with the assumption that the posterior cerebellum is involved in the inhibition of movement execution during imagination.     

Functional neuroimaging of dressing-related skills

Restoration of motor function following stroke involves reorganization of motor output through intact pathways, with compensatory brain activity likely variable by task. One class of motor tasks, those involved in self-care, is particularly important in stroke rehabilitation. Identifying the brain areas that are engaged in self-care and how they reorganize after stroke may enable development of more effective rehabilitation strategies. We piloted a paradigm for functional MRI assessment of self-care activity. In two groups, young adults and older adults, two self-care tasks (buttoning and zipping) produce activation similar to a bimanual tapping task, with bilateral activation of primary and secondary motor cortices, primary sensory cortex, and cerebellum. Quantitative differences include more activation of sensorimotor cortex and cerebellum in buttoning than bimanual tapping. Pilot subjects with stroke showed greater superior parietal activity across tasks than controls, potentially representing an increased need for sensorimotor integration to perform motor tasks.     

Sensitivity and specificity of seizure-onset zone estimation by ictal magnetoencephalography

Purpose: Ictal video–electroencephalography (EEG) is commonly used to establish ictal onset‐zone location. Recently software development has enabled systematic studies of ictal magnetoencephalography (MEG). In this article, we evaluate the ability of ictal MEG signals to localize the seizure‐onset zone. Methods: Twenty‐six patients underwent ictal MEG and epilepsy surgery. Prediction of seizure‐onset zone by ictal and interictal MEG was retrospectively compared with ictal‐onset area found by intracranial EEG in 12 patients. The specificity and sensitivity of the prediction were calculated at hemisphere‐lobe (HL) and at hemisphere‐lobe‐surface (HLS) levels. Key Findings: The sensitivity of ictal MEG source localization was 0.958 on HL and 0.706 on HLS levels, and its specificity was 0.900 on HL and 0.731 on HLS levels. The interictal MEG dipole cluster, defined as >10 dipoles on one lobar surface, had sensitivity of 0.400 and specificity of 0.769. Ictal MEG was equally sensitive and specific on dorsolateral and nondorsolateral neocortical surfaces up to a depth of 4 cm from the scalp. Significance: Sources of ictal‐onset MEG signals and interictal dipole clusters are essentially equally specific in estimation of the ictal‐onset zone on lobar surface resolution, but ictal MEG is more sensitive. On the lobe resolution, ictal MEG estimates ictal‐onset zone with high sensitivity and specificity.     

Evidence for fast, low-level motor resonance to action observation: an MEG study

Lateralized magnetic fields were recorded from 12 subjects using a 151 channel magnetoencephalography (MEG) system to investigate temporal and functional properties of motor activation to the observation of goal-directed hand movements by a virtual actor. Observation of left and right hand movements generated a neuromagnetic lateralized readiness field (LRF) over contralateral motor cortex. The early onset of the LRF and the fact that the evoked component was insensitive to the correctness of the observed action suggest the operation of a fast and automatic form of motor resonance that may precede higher levels of action understanding.     

Ictal magnetoencephalographic discharges from elementary visual hallucinations of status epilepticus

PURPOSE: To report the rare opportunity to study ictal magnetoencephalography (MEG) in a 26 year old man with simple partial status epilepticus that presented as elementary visual hallucinations (EVHs) in the right upper visual field. METHODS: The patient described his EVHs as "snowing on TV," "flickering lights," and "rotating coloured balls" that continued for several days. MEG and simultaneous EEG were recorded twice: during an episode of EVHs (ictal recordings) and after EVHs were controlled by medications (interictal recordings). RESULTS: During EVHs, MEG showed continuous periodic epileptiform discharges over the left posterior superior temporal region, while simultaneous EEG showed rhythmic theta waves and sporadic spikes over the left temporal region. The MEG discharge consisted of a three phase spike complex. Equivalent current dipoles (ECDs), modelled from spike complexes, localised in the left superior temporal area. After drug treatment controlled the EVHs, interictal MEG and EEG showed rare spikes over the same left temporal region. The average ictal ECD moment (mean (SD)) (128.7 (32.8 nAm)) was significantly weaker than the average interictal ECD moment (233.0 (63.9) nAm) (p<0.05). CONCLUSIONS: The continuous, periodic, and clustered discharges seen on ictal MEG were the sources of EVH. The weaker ictal ECD sources were frequently not detected by scalp EEG, while the stronger interictal sources, presumably originating from an extensive interictal zone, were sufficiently large to be seen as EEG spikes.     

Efficacy of Thyrotropin-Releasing Hormone in the Treatment of Intractable Epilepsy

Purpose : The ictal EEG and magnetoencephalogram (MEG) for gelastic seizures were recorded in a 4-year-old girl with tuberous sclerosis. The sites of origin for the seizure activities were investigated by using an equivalent current dipole (ECD) with the MEG.
Methods : EEG and MEG were recorded simultaneously under the administration of diazepam (DZP). The MEG recording was performed on a system consisting of an array of 64 sensors uniformly distributed over the patient's whole head (CTF, Canada), and the estimated ECDs were superimposed on the magnetic resonance imaging (MRI) images (Siemens, 1.5 Tesla).
Results : Two laughing attacks lasting 5 s each were documented. The ictal EEG showed gradually increasing 11–Hz rhythmic α activities with dominance over the frontocentral areas bilaterally, followed by irregular spike-and-wave discharges. The ictal MEG detected bilateral frontal rhythmic sharp waves before the appearance of the activities on the EEG. The estimated ECDs were localized in the deep white matter of the right frontal lobe on the MRI. However, those dipoles did not coincide with the locations of her cortical tubers.
Conclusions : Although gelastic seizures accompanied with hypothalamic hamartomas are well known, several reports have suggested a temporal or frontal lobe origin for gelastic seizures. In this patient, the ECD indicated that the seizures originated in the frontal lobe, although ictal scalp EEG recordings could not determine the precise focus. Thus, in cases in which the use of ictal scalp EEG fails to show the sites of origin for the seizures, it is recommended that the origins be estimated by using the non-invasive method of ictal MEG analysis.     

Involuntary motor activity in pianists evoked by music perception

Pianists often report that pure listening to a well-trained piece of music can involuntarily trigger the respective finger movements. We designed a magnetoencephalography (MEG) experiment to compare the motor activation in pianists and nonpianists while listening to piano pieces. For pianists, we found a statistically significant increase of activity above the region of the contralateral motor cortex. Brain surface current density (BSCD) reconstructions revealed a spatial dissociation of this activity between notes preferably played by the thumb and the little finger according to the motor homunculus. Hence, we could demonstrate that pianists, when listening to well-trained piano music, exhibit involuntary motor activity involving the contralateral primary motor cortex (M1).