Search

The synthetic aperture magnetometry (SAM) is a spatially selective beamformer, which transforms neuromagnetic signals into units of dipole moment on a per-voxel basis. We applied this technique to demonstrate the tomographic distribution of the power calculated from the spontaneous magnetoencephalogram (MEG) activities in a patient with a focal cerebral ischemia.The distribution of spontaneous MEG activity was affected by the changes in the regional cerebral blood flow (rCBF) and also by the presence of magnetic resonance image (MRI)-documented lesion. The present study for the first time demonstrated the altered patterns in the tomography of spontaneous MEG activity at different frequency bands, i.e. delta, alpha and beta bands, in a stroke patient which may elucidate an important implication in the pathoneurophysiology associated with cerebral ischemia. [Copyright &y& Elsevier]

Abstract: Synthetic aperture magnetometry (SAM) was applied to investigate changes in the mechanism of cerebral motor control in patients with tumors around the central sulcus in relation to the clinical relevance. MEG records were made during a resting state and a repetitive hand grasping task in patients with brain tumors around the central sulcus and in four control subjects. Topographic appearance of abnormal focal slowing in the delta, theta, and alpha bands (N =10) and event related desynchronizations (ERD) in the alpha, beta, and low gamma bands during the motor tasks (N =6) were analyzed statistically with SAM in relation to clinical signs and symptoms. Distribution of enhanced focal delta activity coincident with the motor cortices responsible for weakness. Volumetric analysis revealed emergence of tumor-related focal delta activity was greater for intra-axial tumors involving subcortical fibers than for other extra-axial tumors. In addition, patients with increased volume of enhanced delta activity exhibited poor functional recovery in the early post-operative period. Beta ERD in patients during affected side hand movement was also localized exclusively to the ipsilateral hemisphere contrary to the normal pattern. The characteristic focal delta distribution and the altered patterns of ERD in the patient group suggest not only close relation of cortical function and existing pathology but recruitment of diverse motor areas which may be required for the effective movement of the affected side. [Copyright &y& Elsevier]

Abstract: The aim of this study is to reveal the oscillatory change and subjective arousal level during simulated driving using synthetic aperture magnetometry (SAM). Subjects were instructed to perform the driving simulation task using a steering wheel, accelerator and brake pedals. The subjective arousal level was estimated using a visual analog scale. The subjective arousal level was reduced and the activities of theta band (4–8 Hz) in frontal areas were increased as driving time advanced. It is well known that the theta wave increases during rest state. Our previous studies also demonstrated that pseudo-Z value in the theta band inversely correlates with subjective arousal level. The present study demonstrated that this relation holds true even during driving state. [Copyright &y& Elsevier]

Abstract: Cerebral occlusive vascular disease has been well investigated in aspect of a risk factor for stroke, however, whether it causes any alteration in brain function is poorly understood. To investigate this, we examined the motor related magnetic field in 20 patients with cerebral occlusive disease (12 with atherosclerotic (AS group) and 8 with non-atherosclerotic lesions (NAS group)) and 7 control subjects, and evaluated the spatial distribution and the intensity (t-value) of event related desynchronization in beta band during hand grasping and finger tapping tasks using synthetic aperture magnetometry. According to the laterality index (L.I.) calculated from peak t-values on both hemispheres, activation pattern was classified into 3 types, as contralateral—(L.I.>0), bilateral—(0.1

The aim of this study was to verify the relation between gamma-band activity and process of function words. We recorded the neuromagnetic signals in six healthy volunteers during silent reading of verbs (verb task) and forming of the past tenses (past-tense task) and investigated the spatio-temporal distribution of event-related desynchronization (ERD) and synchronization using synthetic aperture magnetometry. In both tasks, ERDs were observed simultaneously at multiple language-related areas. The left junctional area of inferior frontal sulcus and precentral sulcus and the left supramarginal gyrus showed stronger and/or longer-lasting ERDs in past-tense task than in verb task. This result suggests that the gamma-activities reflect the syntactic process of words. [Copyright &y& Elsevier]

Using synthetic aperture magnetometry (SAM), we examined the spatial distribution of frequency changes in magnetoencephalography signal rhythms on individual magnetic resonance images following somatosensory stimulation. SAM is a novel statistical spatial filtering method that uses an adaptive beamformer. Electrical stimulation of the right median nerve demonstrated high-frequency event-related synchronization (ERS) in the 50–200-Hz range, consistently localized in the contralateral primary sensorimotor area in all subjects (n=7). Event-related desynchronization (ERD) was demonstrated in the 8–13, 13–25 and 25–50-Hz ranges bilaterally in the area surrounding the central sulcus. The differences in the spatial distribution as well as the frequency bands between ERS and ERD suggest that ERS and ERD reflect the responses of different cell assemblies rather than a frequency shift of the same cell assembly. [Copyright &y& Elsevier]