Detection of epileptic spikes by magnetoencephalography and electroencephalography after sleep deprivation.

INTRODUCTION: In diagnosis of epilepsies electrophysiological findings play a key role. While spontaneous electroencephalography (EEG) and EEG with sleep deprivation (EEGsd) are widely evaluated and used, application of magnetoencephalography (MEG) in this field is primarily limited to presurgical assessment of focal epilepsies. METHODS: In this study we retrospectively compared MEG (M/EEG) and EEGsd in 63 (55) patients with focal and generalized epilepsy with regard to occurrence of epileptic spikes. RESULTS: MEG could record epileptic spikes in 38 patients (60%), while EEGsd recorded spikes in only 32 patients (51%). In a group of 55 patients simultaneous MEG/EEG (M/EEG) was able to record spikes in 38 patients (71%) compared to epileptic spikes in 28 patients (51%) recorded by EEGsd. In a subgroup of 17 MR-negative patients simultaneous M/EEG could record epileptic spikes in all patients, while EEGsd was successful in only 11 (64%) of them. CONCLUSION: In this study, MEG showed a tendency to record epileptic spikes in more patients than EEGsd. Furthermore, simultaneous M/EEG has been shown to be especially successful in detection of epileptic spikes in patients with MR-negative epilepsy. This might at least in parts be explained by neocortical predominance of MR-negative epilepsy. Thus, this study motivates prospective studies to evaluate the substitutability of EEGsd by MEG more extensively.

Spatial intralobar correlation of spike and slow wave activity localisations in focal epilepsies: a MEG analysis.

12 patients with focal epilepsy were examined by magnetoencephalography (MEG). Source localisations of interictal epileptiform activity (spikes) yielded clear results. Slow wave dipole density in the frequency range from 2 to 6 Hz, using time selections from an automatic principal component analysis (PCA), was calculated. Results of spike and slow wave dipole density localisations were superimposed on MR-images of each patient. Slow wave dipole densities were increased close to spike localisations. Distances between spike center of mass and slow wave maxima were calculated, average mean distance was 2.0 cm. Independant of the localisation in either TLE or ETLE a concordance of slow wave and spike localisations were found. Slow wave localisations were found in patients with lesions in MRI and patients with no abnormalities on the MRI. In comparison to healthy subjects, slow wave dipole density in patients with epilepsy was clearly increased. The localisation of slow wave dipole density yielded additional important information and may contribute to defining the irritative zone.

Comparison of clonidine to sleep deprivation in the potential to induce spike or sharp-wave activity.

OBJECTIVE: This study aimed to investigate previously observed side effects, i.e. increased epileptic activity during clonidine medication. The safety and effectiveness of clonidine as spike inducing agent compared to sleep deprivation were tested. METHODS: Patients suffering from drug-resistant localization related epilepsy took part in 3 magnetoencephalography (MEG) sessions. One session was recorded without any activating measures. The other two sessions were either performed after sleep deprivation or after medication with clonidine. Target parameter was the number of spikes or sharp-waves during a 30 min recording period. RESULTS: About 67% of the patients showed increased spike activity after clonidine, whereas sleep deprivation increased the number of spikes in 33%, and 29% of the patients did not show any activation at all. Clonidine was most effective in temporal lobe epilepsy, when the focus was located in the right hemisphere, and when clonidine serum concentrations were ranging between 0.6 and 1.0 ng/ml. CONCLUSIONS: This study showed for the first time that clonidine can be considered an effective spike or sharp-wave inducing drug that is superior to the potency of sleep deprivation. SIGNIFICANCE: The administration of clonidine increases the probability of recording ictal and interictal epileptic activity during limited acquisition time.

Epilepsy surgery, resection volume and MSI localization in lesional frontal lobe epilepsy.

To verify whether interictal noninvasive information detected by magnetoencephalography (MEG) recordings can contribute to localize focal epileptic activity relevant for seizure generation in lesional frontal lobe epilepsy, magnetic source imaging (MSI) localizations of epileptic discharges were compared to the extent of neurosurgical resection and postoperative outcome. Preoperative MEG spike localizations were displayed in postoperative magnetic resonance imaging (MRI) scans to check whether dipole sites were located within the resection cavity. Moreover, MEG localizations were compared with results of prolonged video-EEG monitoring and, in three cases, with invasive EEG recordings. Our results in five cases with lesional frontal lobe epilepsy showed that good surgical outcome could be achieved in those patients where the majority of MEG spike localizations were located within the resected brain volume.

Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases.

Epilepsy surgery is based upon the minute assessment of brain tissue generating epileptic activity. A number of diagnostic methods are employed in the process of presurgical evaluation, supplying information on various morphological and functional aspects, ultimately integrated into the general result fundamental to the final treatment decision. Magnetic source imaging (MSI), combining structural (MRI) and functional (MEG) data, has been playing an increasingly important role among the tools of presurgical epilepsy evaluation. However, in spite of a considerable number of publications, the samples used have hardly exceeded 50 cases. Therefore, we present a synopsis of 455 epilepsy patients who underwent MSI investigations. Analysis of this substantial data revealed that the average sensitivity of MEG for specific epileptic activity was 70%. Among 131 patients who underwent surgical therapy in addition to antiepileptic drug medication, MSI identified the lobe to be treated in 89%, with results for extratemporal cases being even superior to those with temporal lobe surgery. Introducing a measure to quantify the contribution of MSI to the general result of presurgical evaluation that was applied to 104 patients, the results showed that MSI supplied additional information in 35% and information crucial to final decision making in 10%. Accuracy as well as contribution findings underlined MSI appropriateness even for extratemporal epilepsies, which otherwise frequently prove difficult with respect to focus localization.

Somatosensory evoked magnetic fields following passive movement compared with tactile stimulation of the index finger.

Cortical processing of passive finger movement was assessed magnetoencephalographically in 12 healthy volunteers and compared with somatosensory evoked magnetic fields (SEF) following tactile stimulation. A new device comprising a clamp-like digit holder facilitated bilateral guidance of the briskly elevated index finger. Both passive movement and tactile stimulation induced activation of the contralateral primary somatosensory (SI) cortex, indicated by six SEF deflections with inter-individually rather consistent peak latencies of 20-230 ms following proprioceptive and 20-300 ms following tactile stimulation. SEF responses to the two stimulus modalities clearly differed with regard to peak latencies, amplitudes and orientations of equivalent current dipoles (ECDs). The strength and orientation of proprioception-related ECDs suggested sequential activation of SI generators, with possible involvement of areas 3a and/or 2 at around 20 ms, area 4 at approximate peak latencies of 65 and 100 ms and area 3b between 150 to 230 ms. Passive movement elicited additional activation of cortical regions outside SI, including the bilateral perisylvian regions and the contralateral cingulate gyrus at latencies of 40-470 and 150-500 ms respectively. The study provides new results with respect to the spatiotemporal analysis of proprioception-related cortical processing and may contribute to a better understanding of the modality-specific organization of the human somatosensory cortex.

A combined study of tumor-related brain lesions using MEG and proton MR spectroscopic imaging.

The purpose of this study is to localize, in cases of brain tumors, pathological magnetic brain activities and to analyze metabolic alterations in functionally abnormal lesions using magnetoencephalography (MEG) and proton magnetic resonance spectroscopic imaging (1H MRSI). The study focused on 10 healthy volunteers and seven patients with common brain tumors, namely astrocytic tumor and meningioma. In spontaneous MEG, the pathological brain activities (slow, fast waves and spikes) were localized using a single equivalent dipole model. After the results of MEG and 1H MRSI were superimposed onto the corresponding MR images, the signal intensities of spectroscopically visible metabolites were analyzed in the regions where the dipoles of the pathological activities were concentrated. Increased slow wave activity was observed in four cases and fast wave or spike activity was significantly increased in one case. These pathological activities were localized in surrounding regions of the bulk of tumors, where mild reduction of N-acetyl aspartate (NAA) and slight accumulation of lactate (Lac) consistently existed. Preserved cortical areas, which are indicated by residual NAA, might be able to generate pathological magnetic activities under lactic acidosis. Such areas could be understood as a border zone between normal and seriously damaged brain tissue by tumors or associated brain edema. This combined technique with the different modalities gives insight into functional as well as metabolic aspects of pathological brain conditions.

Alteration of the somatosensory cortical map in peripheral mononeuropathy due to carpal tunnel syndrome.

Substantial plasticity of the mature mammalian somatosensory cortex was demonstrated after deprivation of sensory input produced by amputation or somatosensory deafferentation. Following transection of the median nerve, adult owl and squirrel monkeys exhibit extensive reorganization in the cortical representation of the hand in areas 3b and 1. In the present study we investigated the possible effect of incomplete median nerve damage on sensory cortex somatotopy in a patient with unilateral carpal tunnel syndrome. We assessed interhemispheric differences of the hand representation in SI by means of magnetic source imaging. Additional intersubject data comparison was performed for specific results on the basis of available normal data from the literature and from own investigations in five healthy volunteers. Our results demonstrated a decreased extension of the cortical zone representing the injured median nerve and suggested invasion of the deprived area by cortical sectors receiving inputs from the little finger (supplied by the ulnar nerve) and from the dorsum of the thumb (innervated by the radial nerve). The study indicates topographic rearrangement of the hand representational zone in the human primary somatosensory cortex in a case of chronic median nerve injury.

Pain-related somatosensory evoked magnetic fields induced by controlled ballistic mechanical impacts.

The purpose of this study was to investigate cortical processing of painful compared with tactile mechanical stimulation by means of magnetoencephalography (MEG) using the novel technique of mechanical impact loading. A light, hard projectile is accelerated pneumatically in a guiding barrel and elicits a brief sensation of pain when hitting the skin in free flight. Controllable noxious and innocuous impact velocities facilitate the generation of different, predetermined stimulus intensities. The authors applied painful as well as tactile mechanical impacts to the dorsum of the second, third, and fourth digit of the nondominant hand. Pain-related somatosensory evoked magnetic fields (SSEFs) were compared with those following tactile stimulation in seven healthy volunteers. Contralateral primary sensory cortical area activation was observed within the first 70 msec after tactile as well as painful stimulus intensities. Only painful impacts elicited SSEF responses assigned to the bilateral secondary sensory cortical regions and to the middle part of the contralateral cingulate gyrus, which were active at latency ranges of 55 to 155 msec and 90 to 220 msec respectively. Additional long-latency responses occurred in these cortical areas as long as 280 msec after painful stimulation in three subjects. In contrast to tactile stimulation, painful mechanical impacts elicited SSEF responses in cortical areas demonstrated to be involved in central pain processing by previous MEG and neuroimaging studies. Because of its similarity to natural noxious stimuli and the possibility of adjustable painful and tactile impact velocities, the technique of mechanical impact loading provides a useful method for the neurophysiologic evaluation of cortical pain perception.

A combined study of tumor-related brain lesions by using magnetoencephalography and 1H magnetic resonance spectroscopic imaging. Technical note.

The purpose of this study was to localize pathological magnetic brain activities and to analyze metabolic alterations in functionally abnormal lesions by using magnetoencephalography (MEG) and (1)H magnetic resonance (MR) spectroscopy in patients with brain tumors. The authors studied 10 healthy volunteers and seven patients who harbored common brain tumors, namely astrocytic tumors and meningioma. In spontaneous MEG the pathological brain activities (slow waves, fast waves, and spikes) were localized using a single equivalent dipole model. After the results of MEG and (1)H MR spectroscopy were superimposed onto the corresponding MR images, the signal intensities of spectroscopically visible metabolites were analyzed in the regions in which the dipoles of the pathological activities were concentrated. Increased slow-wave activity was observed in four cases, and fast-wave or spike activity was significantly increased in one case each, respectively. These pathological activities were localized at almost the same cortical areas adjacent to the bulk of tumors, where mild reduction of N-acetyl aspartate (NAA) and slight accumulation of lactate consistently existed. Preserved and metabolically active cortical areas, which are indicated by residual NAA, might be able to generate pathological magnetic activities under lactic acidosis. Such an area could be understood as a border zone between normal brain tissue and brain tissue that has been seriously damaged by tumors or associated edema, which should be intensively treated. This combination of imaging techniques gives insight into functional as well as metabolic aspects of pathological brain conditions.

Responses to silent Kanji reading of the native Japanese and German in task subtraction magnetoencephalography.

The neuromagnetic activities evoked by semantic processing were localized by magnetoencephalography (MEG). We observed distinct time courses of the activities in native speaking Japanese subjects (Japanese speaker) and German subjects (German speaker) during silent reading of Japanese letters; Kanji and meaningless figures made by deforming the Arabian letters. There were significant differences in amplitude of the activities between Kanji and meaningless figure stimuli. The responses with meaningless figure stimuli were subtracted from those with Kanji stimuli to demonstrate the semantic responses. Earlier responses peaked at about 273.3+/-50. 8 and 245.0+/-23.8 ms (mean+/-S.D.) and were mainly located in the right fusiform gyrus (FuG) in the Japanese and German speakers, respectively. All the Japanese speakers constantly showed additional later responses in the left superior temporal gyrus (STG) and the supramarginal gyrus (SmG) at approximately 616.1+/-105.5 ms, whereas no further activity was observed in the German speakers who did not know the meaning of each Kanji. Because the later responses in the STG and SmG in the Japanese speakers were only observed in their dominant hemisphere, we believe the source of these responses to be part of the neural basis of Kanji semantic processing. The task subtraction MEG analysis could be a powerful method to discriminate distinct responses and visualize the neural networks involved in semantic processing.

Localization analysis of neuronal activities in benign rolandic epilepsy using magnetoencephalography.

Benign epilepsy of childhood with rolandic spikes (BECRS) is an electroclinical syndrome characterized by partial sensorimotor seizures with centrotemporal spikes. We report a detailed localization analysis of spontaneous magnetic brain activities in seven BECRS patients using magnetoencephalography (MEG). All patients had BECRS diagnosis with typical seizures and electroencephalographic findings and five patients had minor psychomotor deficits. MEG was recorded over both parieto-temporal regions using a 2x37-channel biomagnetic system. The collected data were digitally bandpass-filtered (2-6, 14-30, or 1-70 Hz) to analyze slow- and fast-wave magnetic activities and rolandic spikes. Slow-wave activity was increased in four hemispheres of three patients. Increased fast-wave activity was found in all five patients with minor neuropsychological deficits. The presence of increased fast-wave magnetic brain activity appeared to cause functional anomalies in the higher brain function processes. In the spike analysis, the dipoles of rolandic spikes which constantly manifested anterior positivity in direction were concentrated in the superior rolandic region in four cases and the inferior rolandic region in three cases. The localizations of increased slow- and fast-wave activities were identical with those of the spikes. The seizure profiles were frequently characterized by the spike locations. Source localizations of the focal brain activities and rolandic spikes by MEG will contribute to the different diagnosis and pathophysiological elucidation of BECRS.