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Objective：To investigate the immediate effects of vagal nerve stimulation (VNS)on the brain functional connectivity of patients with drug ⁃ resistant epilepsy (DRE)and explore the mechanism by whichVNS inhibits epileptic seizures. Methods： Magnetoencephalography (MEG)data were collected from 14 healthy subjects in a resting state and from 14 DRE patients in both resting and stimulated states. The changes in brain functional connectivity induced by immediate VNS were analyzed in six frequency bands. Results：In the resting state，DRE patients showed significantly enhanced functional connectivity compared to healthy subjects. When VNS occurred，DRE patients exhibited significantly reduced functional connectivity，including the connections between the left middle frontal gyrus and the right olfactory cortex and the connections between the left thalamus and the surrounding cortex of the right calcarine fissure in the theta frequency band，and the connections between the left thalamus and the left temporal polar middle temporal gyrus in the alpha frequency band. Conclusion：Immediate VNS can reduce the brain functional connectivity of DRE patients，thereby reducing the vulnerability of the brain network to seizures. This might be an important mechanism by which VNS modulates the inhibition of epileptic seizures in DRE patients. [ABSTRACT FROM AUTHOR]

Objective To preliminarily explore the correlation of positive occipital sharp transients of sleep (POSTS) in MEG and EEG, and summarize the characteristics of MEG POSTS morphology and localization. Methods The MEG and EEG signals were simultaneously recorded in 5 healthy subjects during sleep, who were recruited from December 2020 to August 2021 in Beijing Tiantan Hospital, Capital Medical University. The features of MEG POSTS and its relationship with EEG POSTS were summarized. Single equivalent current dipole (ECD) model was used to conduct source imaging for POSTS. Results About 564 EEG POSTS during sleep were recorded in 5 subjects. There were 359 simultaneous MEG POSTS in occipital region after exclusion of the POSTS overlapping with heart beat in ECG. The appearance rate of MEG POSTS was 73.42% (359/489). The MEG POSTS showed great variability in morphology. MEG POSTS dipoles were located mainly in bilateral midline regions of occipital lobe, including calcarine sulcus, lingual gyrus and cuneus; some in other parts of occipital lobe away from midline regions, such as medial occipitotemporal gyrus, lateral occipitotemporal gyrus and lateral occipital cortices; and a small portion in bilateral parietooccipital sulcus and precuneus. Conclusions MEG POSTS has characteristics different from EEG POSTS, so it is important to recognize POSTS correctly in clinical MEG reading to discriminate between physiological and pathological waves and provide precise information for presurgical evaluation of epilepsy.

BACKGROUND: Spinal cord injury is a kind of common central nervous system disease, causing dysfunction below the injury plane, which affects patient’s living quality and endangering human’s life seriously. The use of motor imagery therapy in the treatment of spinal cord injury is a new rehabilitation field in recent years, and it is a kind of rehabilitation treatment technology with a great development potential. OBJECTIVE: To review the basic principles of motor imagery, the possible mechanism of motor imagery applied to spinal cord injury and the research progress. METHODS: “Spinal cord injury, motor imagery” were used as search terms to retrieve articles on PubMed, Web of Science, CNKI, and Wanfang databases from inception to September 2021. The author excluded the articles that were not correlated with the research purpose, were repetitive, and had low credibility, and summarized the 94 articles that finally met the standard. RESULTS AND CONCLUSION: (1) Motor imagery first was put forward in the 1950s, and then it is identified that motor imagery is a special kind of movement function status, and is repeatedly simulation and rehearse some movement of patients with a mental state. It exists in memory, activates the motor memory center, and without any obvious motor output, and follows the principle of central motion control. (2) The theoretical model of motor imagery therapy is generally recognized as psycho-neuromuscular theory, which holds that motor imagery is similar to the neuromuscular activity induced by motor execution. (3) The mechanism of motor imagery therapy for spinal cord injury is unclear. For patients with spinal cord injury, because brain structure is not damaged, the patient’s ability of motor imagery should be properly preserved. The current studies show that the mechanism may be that spinal cord injury patients and healthy people could activate similar brain regions. In patients with spinal cord injury, similar brain regions are activated by motor imagery and motor execution. Patients can induce the development of central nerve plasticity and functional reorganization through continuous motor imagery training, which can promote the recovery of function. (4) Clinically, current studies have shown that motor imagery training can relieve neuropathic pain, improve motor and bladder function in patients with spinal cord injury. Motor imagery therapy as an adjuvant therapy should be adopted in conventional rehabilitation programs for patients with spinal cord injury. However, there is high heterogeneity in clinical efficacy, and further research is necessary. (5) Brain computer interface can convert the signals generated during the patient’s motor imagery into driving signals to control external devices to achieve the re-movement of paralyzed limbs. The development of motor imagery with brain computer interface is considered to be a revolutionary change in rehabilitation after spinal cord injury and has a very good development prospect. [ABSTRACT FROM AUTHOR]

Objective To preliminarily explore the correlation of positive occipital sharp transients of sleep (POSTS) in MEG and EEG, and summarize the characteristics of MEG POSTS morphology and localization. Methods The MEG and EEG signals were simultaneously recorded in 5 healthy subjects during sleep, who were recruited from December 2020 to August 2021 in Beijing Tiantan Hospital, Capital Medical University. The features of MEG POSTS and its relationship with EEG POSTS were summarized. Single equivalent current dipole (ECD) model was used to conduct source imaging for POSTS. Results About 564 EEG POSTS during sleep were recorded in 5 subjects. There were 359 simultaneous MEG POSTS in occipital region after exclusion of the POSTS overlapping with heart beat in ECG. The appearance rate of MEG POSTS was 73.42% (359/489). The MEG POSTS showed great variability in morphology. MEG POSTS dipoles were located mainly in bilateral midline regions of occipital lobe, including calcarine sulcus, lingual gyrus and cuneus; some in other parts of occipital lobe away from midline regions, such as medial occipitotemporal gyrus, lateral occipitotemporal gyrus and lateral occipital cortices; and a small portion in bilateral parietooccipital sulcus and precuneus. Conclusions MEG POSTS has characteristics different from EEG POSTS, so it is important to recognize POSTS correctly in clinical MEG reading to discriminate between physiological and pathological waves and provide precise information for presurgical evaluation of epilepsy. [ABSTRACT FROM AUTHOR]

The ultimate goal of neurosurgery is to remove the lesion to the greatest extent while retaining neurological function. The preservation of motor function, sensory function, especially language function is of great significance to patients. So preoperative and intraoperative functional mapping has important guidance for surgery. The current invasive method⁃intraoperative direct electrical stimulation (DES) is still the "gold standard" for language mapping and lateralization, while non⁃invasive method such as functional magnetic resonance (fMRI), diffusion tensor imaging (DTI), magnetoencephalography (MEG) and navigated transcranial magnetic stimulation (nTMS) are easy to operate and can be used for preoperative positioning, postoperative follow⁃up and review. Multimodal functional assessment can improve the accuracy of preoperative language mapping. This article intends to review the positioning methods of language function areas and compare the advantages and disadvantages of various methods. DOI:10.3969/j.issn.1672⁃6731.2020.11.003

The ultimate goal of neurosurgery is to remove the lesion to the greatest extent while retaining neurological function. The preservation of motor function, sensory function, especially language function is of great significance to patients. So preoperative and intraoperative functional mapping has important guidance for surgery. The current invasive method - intraoperative direct electrical stimulation (DES) is still the "gold standard" for language mapping and lateralization, while non-invasive method such as functional magnetic resonance (fMRI), diffusion tensor imaging (DTI), magnetoencephalography (MEG) and navigated transcranial magnetic stimulation (nTMS) are easy to operate and can be used for preoperative positioning, postoperative follow-up and review. Multimodal functional assessment can improve the accuracy of preoperative language mapping. This article intends to review the positioning methods of language function areas and compare the advantages and disadvantages of various methods. [ABSTRACT FROM AUTHOR]

Objective To evaluate the diagnostic value of magnetoencephalography (MEG) in localizing the seizure focus and in predicting outcome to surgical resections of insular lobe epilepsy. Methods Eight patients who had been diagnosed as refractory insular lobe epilepsy in Xuanwu Hospital were selected. All patients had pre-surgical work-ups, including MRI, video EEG (VEEG) and MEG to localize epileptogenic area, and 4 of them had been implanted intracranial electrodes to identify epileptogenic zone and underwent operation under the monitoring of electrocorticography (ECoG). They were followed up after surgery to evaluate the prognosis, and further to evaluate the diagnostic value of MEG on insular lobe epilepsy. Results Eight patients had surgeries under the guide of preoperative MEG examination. Five of them had been localized in insular or anterior insular lobe and 3 of them had been localized around the insular lesion by MEG. According to postoperative Engel classification, 6 was Ⅰ, one was Ⅱ, and one was Ⅳ. Conclusions MEG provides useful localizing information and predicts surgical outcome of insular lobe epilepsy. doi: 10.3969/j.issn.1672-6731.2014.11.011

Objective To investigate the prognostic factors of surgical operation in patients with epilepsy induced by focal cortical dysplasia (FCD). Methods The clinical data of 42 patients with epilepsy induced by pathological proved FCD, were analyzed retrospectively. Postoperative follow-up for 12 to 36 months, Engel classification of assessing the prognosis of patients, application of Logistic regression analysis to investigate the factors influencing the prognosis of surgery. Results 27 patients (64.3%) were Engel class Ⅰ, 6 patients (14.3%) were Engel class Ⅱ, 6 patients (14.3%) were Engel class Ⅲ, 3 patients (7.1%) were Engel class Ⅳ. Logistic regression showed that inconsistency of MEG and surgical range (OR=6.063, 95%CI 1.168-31.482, P<0.05) and incomplete resection (OR=7.739, 95%CI 1.447-41.398, P<0.05) were independent prognostic factors. Gender, age, course of disease, the history of febrile seizure, the location of epileptogenic zone, brain MRI and type of FCD were not statistically significant. Conclusion The operative prognoses of the patients with epilepsy induced by FCD are associated with consistency of MEG and surgical range, complete resection of epileptogenic zone. [ABSTRACT FROM AUTHOR]

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Objective To analyze the activity differences between patients with left temporal lobe epilepsy(LTLE)and normal controls by magnetoencephalography(MEG)synthetic aperture magnetometry(SAM),and assess the alteration of interictal brain activity in patients with LTLE. Methods Resting-state MEG data were collected from 20 patients with LTLE and 20 healthy volunteers(normal control group).The SAMg2 Z-map of each subject were calculated by the SAMg2 script of the CTF software.After the calculation,the SAMg2 Z-map of each subject were registered with their corresponding 3D MRI.Results Compared with the normal control group,significantly elevated SAMg2 signals were found in left temporal lobe epilepsy patients in the left temporal lobe and medial structures.Marked decreases of SAMg2 signals were found in wide extratemporal lobe, such as the bilateral visual cortex.Abnormal regions of left temporal lobe epilepsy patients were significantly associated with frequency of seizures.There were no significant differences in age and gender between the two groups.Conclusion Left temporal lobe epilepsy could be a multifocal disease,including complex epileptic networks and brain dysfunction networks. [ABSTRACT FROM AUTHOR]

Objective To explore the consistency of magnetoencephalography (MEG) resting-state neural networks and electrocorticography (ECoG) locating. Methods 16 patients with refractory epilepsy were recruited and MEG resting-state neural networks and ECoG were located before surgical operation to contrast the consistency. Results Spikes were observed in 16 patients, and located focally in 10 and sporadically 6 by Dipole. Single focus in 11 patients and multiple lesions in 5 patients were located by SAM. The resting state brain network of all patients were abnormal, the sensitivity was 100% (16/16). The coincidence rate was 62.5% (10/16) between Dipole and ECoG, 68.7% (10/16) between SAM and ECoG, 81.2% (13/16) between MEG and ECoG locating seizure onset zones, 100% between MEG and ECoG locating resting state brain network. Conclusion MEG resting-state neural networks may locate locate seizure onset zones, and contribute epilepsy operation. [ABSTRACT FROM AUTHOR]

Objective To evaluate the diagnostic value of magnetoencephalography (MEG) in localizing the seizure focus and in predicting outcome to surgical resections of insular lobe epilepsy. Methods Eight patients who had been diagnosed as refractory insular lobe epilepsy in Xuanwu Hospital were selected. All patients had pre-urgical work-ps, including MRI, video EEG (VEEG) and MEG to localize epileptogenic area, and 4 of them had been implanted intracranial electrodes to identify epileptogenic zone and underwent operation under the monitoring of electrocorticography (ECoG). They were followed up after surgery to evaluate the prognosis, and further to evaluate the diagnostic value of MEG on insular lobe epilepsy. Results Eight patients had surgeries under the guide of preoperative MEG examination. Five of them had been localized in insular or anterior insular lobe and 3 of them had been localized around the insular lesion by MEG. According to postoperative Engel classification, 6 was I, one was II, and one was IV. Conclusions MEG provides useful localizing information and predicts surgical outcome of insular lobe epilepsy. [ABSTRACT FROM AUTHOR]

Brain-computer interaction (BCI) is a transformative human-computer interaction, which aims to bypass the peripheral nerve and muscle system and directly convert the perception, imagery or thinking activities of cranial nerves into actions for further improving the quality of human life. Magnetoencephalogram (MEG) measures the magnetic field generated by the electrical activity of neurons. It has the unique advantages of non-contact measurement, high temporal and spatial resolution, and convenient preparation. It is a new BCI driving signal. MEG-BCI research has important brain science significance and potential application value. So far, few documents have elaborated the key technical issues involved in MEG-BCI. Therefore, this paper focuses on the key technologies of MEG-BCI, and details the signal acquisition technology involved in the practical MEG-BCI system, the design of the MEG-BCI experimental paradigm, the MEG signal analysis and decoding key technology, MEG-BCI neurofeedback technology and its intelligent method. Finally, this paper also discusses the existing problems and future development trends of MEG-BCI. It is hoped that this paper will provide more useful ideas for MEG-BCI innovation research.

Speech comprehension is a central cognitive function of the human brain. In cognitive neuroscience, a fundamental question is to understand how neural activity encodes the acoustic properties of a continuous speech stream and resolves multiple levels of linguistic structures at the same time. This paper reviews the recently developed research paradigms that employ electroencephalography (EEG) or magnetoencephalography (MEG) to capture neural tracking of acoustic features or linguistic structures of continuous speech. This review focuses on two questions in speech processing: (1) The encoding of continuously changing acoustic properties of speech; (2) The representation of hierarchical linguistic units, including syllables, words, phrases and sentences. Studies have found that the low-frequency cortical activity tracks the speech envelope. In addition, the cortical activities on different time scales track multiple levels of linguistic units and constitute a representation of hierarchically organized linguistic units. The article reviewed these studies, which provided new insights into the processes of continuous speech in the human brain.

Integrating different visual features into a coherent object is a central challenge for the visual system, which is referred as the binding problem. Firstly, this review introduces the conception of the binding problem and the theoretical and empirical controversies regarding whether and how the binding processes are implemented in visual system. Although many neurons throughout the visual hierarchy are known to code multiple features, feature binding is recruited by visual system. Feature misbinding (or illusory conjunction) is probably the most striking evidence for the existence of the binding mechanism. Next, this review summarizes some critical issues in feature binding literature, including early binding theories, late binding theories, neural synchrony theory, the feature integration theory and re-entry processing theory. Feature binding is not a fully automatic or bottom-up processing. Reentrant connection from higher visual areas to early visual cortex (top-down processes) plays a critical role in feature binding, especially in active feature binding (i.e. feature misbinding). In addition, with electrophysiology, electroencephalography (EEG), magnetoencephalography (MEG) and transcranial electric stimulation (tEs) approaches, recent studies explored both correlational and causal relations between brain oscillations and feature binding, suggesting that brain oscillations are of great importance for feature binding. Finally, this review discusses some potential problems and open questions associated with visual feature binding mechanisms which need to be addressed in future studies.

Objective: To investigate the value of morphometric analysis program (MAP) combined with magnetoencephalogram (MEG) in the localization of epileptogenic foci in MRI-negative pharmacoresistant focal epilepsy (MNPFE) patients. Methods: A total of 42 consecutive MNPFE patients from Epilepsy center, Xuanwu Hospital, Capital Medical University from January 2015 to December 2016 were enrolled. The analysis process of MAP and magnetoencephalography (MEG) were performed independently. When the MAP+ region and the MEG+ region was in the same lobe, the MAP+ region was defined as the MAP+MEG+ region. The analysis results of MAP and MEG were used to do correlation analysis with surgical outcomes separately or simultaneously. Results: The positive rate of MAP was 69% (29/42), and the complete resection of MAP+ region was significantly associated with seizure-free outcome ( P= 0.027). The positive detection rate of MEG was 100% (42/42), and there was no significant association between the complete resection of MEG+ region and seizure-free outcome ( P= 0.517). The positive rate of MAP+MEG+ was 43% (18/42), and the complete resection of MAP+MEG+ region was significantly associated with seizure-free outcome ( P= 0.009). Conclusion: The combination of MAP which indicates subtle structural abnormalities and MEG which pictures electrophysiological features could probably achieve better epileptogenic foci localization in MNPFE patients.

This paper presents a feature extraction method based on multivariate empirical mode decomposition (MEMD) combining with the power spectrum feature, and the method aims at the non-stationary electroencephalogram (EEG) or magnetoencephalogram (MEG) signal in brain-computer interface (BCI) system. Firstly, we utilized MEMD algorithm to decompose multichannel brain signals into a series of multiple intrinsic mode function (IMF), which was proximate stationary and with multi-scale. Then we extracted and reduced the power characteristic from each IMF to a lower dimensions using principal component analysis (PCA). Finally, we classified the motor imagery tasks by linear discriminant analysis classifier. The experimental verification showed that the correct recognition rates of the two-class and four-class tasks of the BCI competition III and competition IV reached 92.0% and 46.2%, respectively, which were superior to the winner of the BCI competition. The experimental proved that the proposed method was reasonably effective and stable and it would provide a new way for feature extraction.

Brain-computer interface (BCI) systems identify brain signals through extracting features from them. In view of the limitations of the autoregressive model feature extraction method and the traditional principal component analysis to deal with the multichannel signals, this paper presents a multichannel feature extraction method that multivariate autoregressive (MVAR) model combined with the multiple-linear principal component analysis (MPCA), and used for magnetoencephalography (MEG) signals and electroencephalograph (EEG) signals recognition. Firstly, we calculated the MVAR model coefficient matrix of the MEG/EEG signals using this method, and then reduced the dimensions to a lower one, using MPCA. Finally, we recognized brain signals by Bayes Classifier. The key innovation we introduced in our investigation showed that we extended the traditional single-channel feature extraction method to the case of multi-channel one. We then carried out the experiments using the data groups of IV-III and IV - I. The experimental results proved that the method proposed in this paper was feasible.

Objective: To explore the clinical application value and feasibility of magnetoencephalography (MEG) in the localization of epileptogenic zone, as compared with scalp electroencephalography., Methods: 69 patients were enrolled in this study, all the patients were examined with MEG and scalp EEG and received operative treatment. During the operation the patients underwent ECoG and deep EEG monitoring and after the operation the follow-up continued 2 - 3 years. Results were evaluated with Engel curative effect grading., Results: Among the 69 patients there was 62 patients whose localization were limited to one lobe with MEG; while only 30 with EEG. We used Engels, grading to define the effectiveness of the operation. 57 among the 69 patients had effective results with an effective rate of 82.61%. When the lateralization of epileptogenic zone in these 57 patients was counted, the concordance rate of preoperative MEG and EEG with intraoperative EEG was 92.98% (53/57) and 33.33% (19/57) respectively with significant difference between MEG and EEG statistically (chi(2) = 30.250, P = 0.000). The scalp EEG of 34 patients with temporal lobe epilepsy showed bilateral temporal lobe epileptiform discharges or generalized spikes, while the epileptogenic foci were shown with MEG only unilaterally and confirmed by operation finally., Conclusions: MEG shows significant value in the lateralization of epileptogenic zone of temporal lobe epilepsy. MEG, with a higher time resolution and space resolution, can help to identify epileptogenic zone and mirror foci. MEG can clarify the spatial relationship between the irritative zone and structural lesions or functional areas.

Objective: To evaluate the applied value of magnetoencephalography (MEG) localization in microsurgery of brain tumors in the region of motor cortex., Methods: From January 2003 to April 2005, 36 patients with 19 meningomas, 14 gliomas, 2 metastases and 1 cavernous angioma underwent MEG and MRI before operation. These individualized functional brain maps were integrated into a neuronavigation system. Preoperative mapping of somatosensory and/or motor cortex was performed, and sites were compared, and all tumors were resected microsurgerically., Results: A space-occupying lesion could change the region of motor cortex in all the patients. Thirty-four cases were resected totally. The patient's myodynamia after operation improved in 19 cases, unchanged in 15 cases, descended in 2 cases., Conclusions: MEG is an effective localization method of function, providing the relationship between the region of motor cortex and the tumor. And it is valuable for accurate planning in the treatment of brain tumors in the region of motor cortex.

Objective: To access the pathological changes of the functional localization of the primary auditory cortex in auditory neuropathy patients using magnetoencephalography (MEG)., Methods: The M100 waves of cortical evoked magnetic fields (AEF) evoked by 0.5, 1, 2, 4, 6, 8 kHz pure tones were measured respectively in 10 auditory neuropathy patients (20 ears) and 15 healthy young subjects (30 ears) using a whole head 306 channel magnetoencephalography (MEG) system. The auditory cortex magnetic source imaging obtained by superimposing functional MEG data on structural magnetic resonance image (MRI)., Results: The M100 sources were obtained in all 15 healthy young subjects in all frequency except for 8 kHz in 16 ears. But in auditory neuropathy patients, the ratio of M100 from 0.5 to 6 kHz were 27.5% (11/40), 22.5% (9/40), 7.5% (3/40), 5% (2/40), 5% (2/40) respectively and no any waves in 8 kHz. The evoked ratio of M100 in low frequency was high and that decreased gradually with increasing of evoked pure tone frequency. The M100 latentencies and amplitudes were longer and lower in patient group than that in control group (P < 0.01)., Conclusions: Auditory neuropathy is an audiology disease with pathological lesions from the VIII cranial nerve to auditory cortex. MEG might become an important reference in decision making for therapies.

In the last few years, brain science has exhibited an explosive growth in hemodynamic/metabolic data on brain function. In particular, PET and functional MRI provide excellent spatial resolution, but their temporal resolutions are severely limited by relatively slow responses of brain metabolism. By contrast, EEG and MEG are able to track modulations of current source activity at millisecond time scales, but suffer from poor spatial resolution. Hence, high-resolution spatiotemporal imaging of brain activity requires integration of information from multiple signal modalities. In this paper we discuss what is known about the physical and physiological basis of the imaging signals, suggest various approaches that have been proposed for integrating information across multiple modalities, and briefly analyze the future directions and remaining challenges in the field of multi-modality integration.

Objective: To evaluate the value of magnetic source imaging (MSI) in the functional localization of the primary auditory cortex., Methods: The M100 waves of cortical auditory evoked magnetic fields (AEFs) evoked by 0.5, 1, 2, 4 and 8 kHz pure tones in 5 subjects and by 2 kHz pure tones in 25 healthy young subjects were measured respectively (16 males and 14 females, with the age from 20 to 32 years old) using a whole head 306 channel magnetoencephalography (MEG) system. The MSI obtained by superimposing functional MEG data on structural magnetic resonance image (MRI) was used to localize the M100 sources on the auditory cortex., Results: The M100 waves of AEFs were clear and replicable in both hemispheres. The M100 sources were localized on the bilateral transverse temporal gyri in all 30 subjects. The localization of M100 on transverse temporal gyri varied with the changes of stimulus frequency. The localization of primary auditory cortex was asymmetrical between bilateral hemispheres, and the left hemisphere M100 dipoles were significantly posterior compared to the right M100 dipoles. The M100 responses appeared significantly earlier to the contralateral stimuli than that to the ipsilateral stimuli in both hemispheres. The dipole positions of M100 were independent of the side of the stimuli., Conclusions: The functional localization of the primary auditory cortex could be determined precisely by magnetic source imaging (MSI) with high spatiotemporal resolution. MSI would hold great promise as a noninvasive tool for the fundamental and clinical research in otology.

In magnetoencepholography(MEG) inverse research, according to the point source model and distributed source model, the neuromagnetic source reconstruction methods are classified as parametric current dipole localization and nonparametric source imaging (or current density reconstruction). MEG source imaging technique can be formulated as an inherent ill-posed and highly underdetermined linear inverse problem. In order to yield a robust and plausible neural current distribution image, various approaches have been proposed. Among those, the weighted minimum-norm estimation with Tikhonov regularization is a popular technique. The authors present a relatively overall theoretical framework Followed by a discussion of the development, several regularized minimum-norm algorithms have been described in detail, including the depth normalization, low resolution electromagnetic tomography(LORETA), focal underdetermined system solver(FOCUSS), selective minimum-norm(SMN). In addition, some other imaging methods, e.g., maximum entropy method(MEM), the method incorporating other brain functional information such as fMRI data and maximum a posteriori(MAP) method using Markov random field model, are explained as well. From the generalized point of view based on minimum-norm estimation with Tikhonov regularization, all these algorithms are aiming to resolve the tradeoff between fidelity to the measured data and the constraints assumptions about the neural source configuration such as anatomical and physiological information. In conclusion, almost all the source imaging approaches can be consistent with the regularized minimum-norm estimation to some extent.

Locating the sources of brain magnetic fields is a basic question in magnetoencephalography (MEG). This question belongs to the indeterminate problem, that is, infinite solutions can be obtained from the equations of the measured small magnetic fields on the detector. Therefore a model of mathematics is needed to give more information. The major models of mathematics are the search method with many dipoles and the Lp minimum norm method. For the first model, if a global search is used, too much calculation time will be spent; if the gradient search is used, the searches usually converge to a local minimun. So other methods are introduced to find out the initial values, and then the gradient search can be used. For the second model, the depth of the brain sources will dependend on the choice of the weight functions which have several different types, and we do not know in advance which type is correct, so that it is difficult to have a good estimation of the depth of the brain sources. To overcome the difficulties, we use the method with three object functions which are the minimum Lp norm, the deviation between the calculated magnetic fields and the measured magnetic fields, and the number of the sources. This method is similar to the minimum norm method, a weight function is also introduced. But this weight function contains many reference variables which have to be determined through the minimization with three object functions. By choosing suitable weight function and its reference variables, the correct estimation of the depth of the brain sources can be achieved.

In magnetic shield room, 9 normal subjects were measured by magnetoencephalography (MEG) and auditory evoked magnetic field (AMF) with superconducting quantum device (SQUID). In our experiment, the magnitudes of MEG were between +100 fT and -100 fT and an AMF evoked with 1 kHz tone burst had 8 stable waves. The main waves were N2, P3, N3 with latencies 65, 118, 175 ms and magnitudes -13, +15, -12 fT. The latencies of waves showed small deviations. The magnitudes of waves were about +/- 15 fT. We also found that the two lateral records of countralateral AMFs have revert waveforms in the last two subjects.