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501.
Y. C. Okada R. Tanenbaum S. J. Williamson L. Kaufman 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1984,56(2):197-205
Summary The primary projection areas in the human somatosensory cortex activated by electrical stimulation of the digits of the hand and the ankle were localized by measuring the magnetic field outside the head contralateral to the side of stimulation. Most of the spatial variation in the amplitude of the field component normal to the scalp could be accounted for by representing each source as a single current dipole in a spherical conducting medium with solely concentric variations in electrical conductivity, although the fit of this model to the data showed some statistically significant deviations. Based on the best-fitting parameter values of the model, we found that the projection areas of the thumb, the index finger, the little finger and the ankle were located at successively more medial positions along the primary somatosensory cortex, at an average depth of 2.2 cm from the scalp surface.This research was supported in part by ONR grant N00014-76-C-0568The preliminary results from the present study were reported at the Sixth Conference on Slow Potentials in the Human Brain held in 1981 (Kaufman et al. 1984) and at the Fourth Workshop on Biomagnetism held in 1982 (Okada 1983) 相似文献
502.
A spatial filter algorithm based on minimum-variance beamforming (synthetic aperture magnetometry (SAM)) was applied to single trial neuromagnetic recordings in order to localize primary somatosensory cortex. Magnetoencephalography (MEG) responses to electrical stimulation of the right and left median nerve were recorded using a whole-head MEG system and localized using both SAM spatial filtering and dipole analysis. Spatial filtering was applied to single trial neuromagnetic recordings to produce 3-dimensional difference images of source power between active (0–50 ms) and control states (−50–0 ms) in the range of 15–300 Hz. Average difference between N20m dipole location and location of maximal increase in power in the SAM images was 3.7 mm (1.5 mm SD) and localized to primary somatosensory cortex. Time-frequency analysis of spatially filtered output for the peak SAM locations showed a brief (10 ms) increase in the 60–100 Hz band coincident with the N20m response and a longer duration (approx. 80 ms) increase in power in the 10–40 Hz band following N20m onset. These results indicate that beamformer based spatial filter methods such as SAM can be used to localize temporally discrete cortical activity produced by median nerve stimulation. 相似文献
503.
John E. Moran Norman Tepley Gary P. Jacobson Gregory L. Barkley M.D. 《Brain topography》1993,5(3):229-240
Summary Electric potential maps and magnetic field maps have been used to study brain electrical activity. During the temporal course of an evoked cortical response, the electrical activity of specific neuronal subpopulations change in a sequential manner giving rise to measurable electrical potentials and magnetic fields. For these potentials and fields, both the amplitude and rate of amplitude change have characteristic, time-dependent waveforms. Presently, amplitude waveforms from multiple locations are used to generate magnetic field and electric potential maps which have been found to be useful in understanding the activity of the neurons which give rise to these maps (Romani 1990). This paper introduces a data transformation technique which results in a derived map that we have termed a "finite difference field map" (FDFM). This mapping technique provides information associated with the rate at which the amplitude of the neuronal electric activity changes. In this paper, some advantages of FDFM analysis are illustrated by application of this technique to the study of the auditory evoked cortical field (AECF) N1m waveform. Using data obtained from normal subjects it will be demonstrated that application of the FDFM technique allows the localization of the primary N1m source at an earlier latency than is possible using the conventional waveform data. The source location determined at an early latency by FDFM analysis was identical to that obtained at later latency from the conventional field data. These data suggest that the primary N1m source is stationary. In addition, analysis of the time sequence of FDFM field maps contains evidence of a second spatially separate source which is co-active with primary N1m source. 相似文献
504.
Setsu Nakatani-Enomoto Yasuo Terao Ritsuko Hanajima Shunichi Matsuda Shinya Ohminami Satomi Inomata-Terada Hideyuki Matsumoto Akihiro Yugeta Tomotaka Yamamoto Jun Goto Masato Yumoto Shoji Tsuji Yoshikazu Ugawa 《Clinical neurology and neurosurgery》2009,111(9):762-765
We describe a 33-year-old man with cyclosporine encephalopathy who showed continuous jerking in the left upper limb due to epilepsia partialis continua. Jerk-locked back averaging (JLA) of magnetoencephalogram disclosed a spike preceding the jerk localized at the hand motor area, whereas JLA of electroencephalogram revealed no premyoclonus spikes. The paired-pulse motor cortical transcranial magnetic stimulation revealed motor cortical hyperexcitability, while the paired-pulse somatosensory evoked potential showed no sensory cortical hyperexcitability. The brain MRI showed a high intensity lesion localized at the hand sensory area. These results suggest that the jerks were produced by discharges at the motor cortex probably disinhibited by the sensory cortical lesion. 相似文献
505.
Lars Arendt-Nielsen Hiroshi Yamasaki Jesper Nielsen Daisuke Naka Ryusuke Kakigi 《Brain research》1999,839(1)
Magnetoencephalographic (MEG) field recordings are unique to detect current dipoles in SI and SII. Few devices are available for painful mechanical stimulation in magnetically shielded MEG rooms. The aim of the present MEG (dual 37-channel biomagnetometer) study was to investigate the location of the cortical generators evoked by painful impact stimuli of different intensities. An airgun was placed outside the shielded MEG room, and small plastic bullets were fired at the arm and trunk of the subjects in the room. The velocity of the bullet was measured and related to the evoked pain intensity. Stimuli were delivered for each of the following three conditions: strong pain intensity elicited from the upper arm and upper trunk; weak pain intensity elicited from the upper trunk. The evoked MEG responses had a major component with the characteristically polarity-reversal deflections indicating a dipole located beneath the coils. The response could be estimated by a single current dipole. When the estimated locations of the dipoles were superimposed on the individual magnetic resonance images (MRIs), consistent bilateral activation of areas corresponding to the secondary sensory cortices (SII) was found. 相似文献
506.
An evaluation of dipole reconstruction accuracy with spherical and realistic head models in MEG. 总被引:4,自引:0,他引:4
MEG forward problem has been solved for about 2000 dipoles placed on the brain surface using a very fine 3-layer realistic model of the head and the boundary element method (BEM). For each dipole, spherical models, one-layer realistic BEM models and coarser 3-layer realistic BEM models, were used to reconstruct the dipole. It was found that the localization bias induced by using a spherical model of the head increased from 2.5 mm in the upper part of the head to 12 mm in the lower part, on average. It was also found that, for the same computing time, a 3-layer model of the head gave on average 2 mm better localization errors than a one-layer model of the head. Orientation errors of less than 20 degrees could only be retrieved with a 3-layer realistic model. Localization and orientation errors highly depended on the dipole position in the brain. 相似文献
507.
508.
赵双任 《生物医学工程学杂志》1999,(4):458-461
脑磁源的定位是脑磁图(Magnetoencephalography,MEG)研究的一个基本问题。该问题属不定问题,即根据探头测量的微小磁场所建立的方程组求得的未知脑磁源有无穷组解。因此需要通过合理的数学模型补充适当信息。目前的两种主要的数字模型为偶极子源搜索法和Lp最小模法。对前者若采用全局搜索费时太多,若采用梯度类搜索法又容易收敛到局部极值点。故一般得用其他方法引导,定出初值,再使用梯度类搜索法 相似文献
509.
510.
LI Jun State Key Laboratory of Modern Optical Instrumentation Center for Optical Electromagnetic Research College of Information Science Engineering Zhejiang University Hangzhou China 《中国生物医学工程学报(英文版)》2001,10(1)
INTRODUCTION Neural currentsources in the human brain produce external magnetic fieldsthatcan be measured noninvasively by using superconducting quantum interferencedevices(SQUID s) .This technique is called Magnetoencephalography(MEG)〔1〕that is becoming a promising technique for brain function research and diagnosis ofsome brain disease〔2〕.In many cases the neuromagnetic sources can be modeled aseveral current dipoles that are appropriate for interpreting postsynaptic potentia… 相似文献