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In the previous article [past life of neural feedback], the neural feedback was roughly combed. We know that neural feedback can be divided into electrophysiological neural feedback and hemodynamic neural feedback according to the types of brain activity signals.

Neurofeedback based on electrophysiological methods can be divided into neurofeedback based on electroencephalogram (EEG). Electroencephalogram (EEG), magnetoencephalogram (MEG) and ECoG.

This issue mainly discusses the technology of magnetoencephalography (MEG).

What is magnetoencephalography (MEG)

Magnetoencephalography (MEG) is a new technique to locate and evaluate the state of brain functional areas by measuring brain magnetic field signals. It has the characteristics of non-invasion and non-injury, and has been applied to the functional research and clinical practice of the human brain.

Physiological basis of magnetoencephalography monitoring brain electromagnetic field

When neurons are excited, time-varying currents are generated through the opening and closing of ion channels inside and outside the membrane. Generally, the potential changes generated by the excitation of a single neuron recorded by neurophysiological means are at the level of tens of millivolts, and the weak magnetic field generated by it is almost impossible to be monitored on the scalp.

Therefore, the formation of monitorable MEG signals requires the superposition of a large number of neuronal discharges.

Based on the neural computing model and empirical data, about 10000-50000 neurons in the same arrangement discharge almost simultaneously, which can generate a monitorable macroscopic electromagnetic signal.

In the human cerebral cortex, there are about 100000 neurons per square millimeter, and each neuron has thousands of synapses on average. At the same time, most neurons in the cortex are perpendicular to the surface of the cortex, and they have the same direction locally, which constitutes the physiological basis for macroscopic monitoring of brain electromagnetic signals.

At the same time, the permeability of all brain tissues, including the skull, is almost the same, which means that the brain is basically "transparent" in the propagation of magnetic field, which provides a powerful driving force for obtaining near-nondestructive real-time detection of neural signals of brain magnetic field.

However, it is very difficult to record these almost lossless neuromagnetic signals. The typical brain magnetic field outside the scalp is in the order of10-100 ft (1ft =10-15t), which is about one billionth of the earth's magnetic field.

How to realize the detection and recording of extremely weak brain magnetic signals under the dynamic interference background of relatively huge earth magnetic field and violent fluctuation of external electromagnetic waves poses a huge technical challenge to human beings.

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The Origin and Development of Magnetoencephalography

18 19, Danish physicist hans oersted discovered that the current in a conductor would generate a magnetic field in the surrounding space.

1969, Dr. Choen completed the first measurement of human brain magnetic field in the magnetic shielding room of his institute by using SQUID sensing device (single channel sensor).

1972, the American magazine Science published Dr. Choen's paper entitled "Detecting the electrical activity of the brain with superconducting magnetic field instrument", which opened a chapter of the mystery of detecting the biological magnetic field of the human brain with superconducting technology.

In the 65438+80s, with the continuous development of computer technology and application software technology, MEG developed from single channel to 37? Channel sensor device, and used for the diagnosis of epilepsy and the study of some brain functions.

In the 1990s of 19, a multi-channel magnetoencephalography measurement system for the whole head was successfully developed, and the magnetic field signals of the whole head can be collected only once. Moreover, it can be superimposed and fused with anatomical image information such as MRI or CT to form the functional anatomical location of the brain, accurately reflect the instantaneous functional state of the brain magnetic field, and is convenient and fast to use, and is applied to clinical research such as neuroscience, neurosurgery, epilepsy, children's nervous system diseases, etc.

From 265438 to the beginning of the 20th century, based on the technical achievements of the whole-head magnetoencephalography system, a fetal magnetoencephalography instrument was successfully developed, which can detect the magnetic field signals of fetal brain, heart and other organs, further promoting the development and application of magnetoencephalography.

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Composition of neural feedback system based on magnetoencephalography

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The neurofeedback system based on magnetoencephalography (MEG) includes four main components, namely: ① magnetic shielding system: to ensure that the brain magnetic signal is not disturbed by external magnetic field; ② Magnetoencephalogram measuring device: mainly composed of superconducting quantum interferometer and detection coil; ③ Stimulation system: such as sound stimulation device and visual stimulation device; ④ Information comprehensive processing system: mainly composed of analysis workstations.

The difference between magnetoencephalography and electroencephalography

Although the signal sources are the same, EEG and MEG have significant differences in signal composition and characteristics.

1. Magnetoencephalography mainly measures the magnetic field generated by intracellular current, and EEG mainly measures the potential generated by extracellular volume current.

2. Magnetoencephalography is used to measure the magnetic field generated by neurons outside the skull, which is not affected by scalp, skull and cerebrospinal fluid, and the location is accurate; Electroencephalogram (EEG) is to measure the potential after the current decays when it passes through the uneven scalp, skull and cerebrospinal fluid. Due to the different conductivity of the above tissues to electricity, the direction of current will deflect when it passes through the above tissues, which leads to inaccurate EEG positioning.

3. The operation of MEG is simple and no electrodes are needed.

4. Economically speaking, magnetoencephalography equipment is expensive, examination cost is high, and EEG is cheap.

Study on the application of magnetoencephalography

I. Basic research

Magnetoencephalography can be used in hearing, vision, language, exercise, information processing of brain cells, fetal brain development, memory, intelligence, sleep and psychological research and many other fields. Magnetoencephalography can be used to analyze several areas in the cerebral cortex related to sensory information processing.

1. Magnetoencephalography can locate auditory pathway, display auditory cranial nerve tissue and measure attention effect.

2. Magnetoencephalography can also clearly locate the visual center, easily measure the brain nerve tissue related to retina and related pathological state, and evaluate the particularity of its visual function.

3. Magnetoencephalography (MEG) can be used to distinguish the areas in the cerebral cortex that process language, which makes the study of language and brain functional areas more convenient and in-depth.

At present, magnetoencephalography has been applied to a series of research in neuroscience, psychiatry and psychology, which provides a very effective research way to reveal the essence of thinking and understand why people become a life with personality, emotion and thought.

Second, the application of clinical medicine

1. Localization of brain functional areas and surgical targets before brain surgery

Before MEG is done, it can only be estimated according to the results of routine imaging examinations such as MRI or CT and clinical experience. When the lesion is closely related to or has invaded the functional area of the brain, the lesion often leads to the displacement or deformation of the normal anatomical structure of the brain, and it is difficult to accurately determine the location of the functional area by conventional imaging examination. Many nervous system diseases have no obvious structural abnormalities, and it is difficult to judge the lesions by imaging detection.

2. Localization of epileptic focus

Epilepsy is a transient brain dysfunction caused by repeated abnormal discharges of brain neurons, and it is the second most persistent disease in neurology after cerebrovascular disease. It is very important to determine whether there are one or more local areas that induce epileptic seizures, to determine the location of these areas, and to determine whether these areas are close to important brain functional areas, so as to adopt the correct surgical plan and obtain satisfactory treatment results.

Research shows that only about? 20% patients with epilepsy can be diagnosed only by imaging data, and the rest need to be located by brain functional imaging. Only 30%-40% of them are located by scalp EEG. The reliability is low, and it can't provide enough positioning and functional information for treatment.

Magnetoencephalography (MEG) can detect epileptic foci with a diameter less than 2mm, and locate them on MRI or ct, forming anatomical or functional morphological images integrating the foci and important functional areas of the brain, which also provides accurate location diagnosis for surgical treatment of intractable epilepsy, and the clinical coincidence rate can reach over 80%.

3. Determination of brain function damage

Magnetoencephalography is also often used to judge neuropathology and functional defects, such as the evaluation of brain trauma, the determination of patients' neurological status, and the evaluation of the effectiveness of neurodrugs.

Friends can also share their relevant experiences and communicate with each other in the message area ~

After sharing, I hope it helps. Remember to like it.

References:

Sheng jingwei, & Jiahong Gao. (202 1). past and future of magnetoencephalography. Physics, 50(7), 7.

[2] Sun Bo. Application of magnetoencephalography in neuroscience. National seminar on the new progress of neuronuclear medicine and neuroscience and working conference of nuclear medicine science popularization experts.

[3] Okadayy C, Lahteenmaki A, Xu C. Clin. Neurophysiology. , 1999, 1 10? (2):2 3 0

[4] Murakami S, Okada Y.J. Physiology. ,2006,575(3):925

[5] Revised edition by Hamalainen, Harry, Ilmoni Lemi and Jarrell. Physics,1993,65 (2): 413

Chang Yi&[6]. Liu Hongyi. (2006). Application of magnetoencephalography in neurosurgery. Journal of Clinical Neurosurgery, 003(00 1), 40-4 1.

[7] Cheng Guang, & Zhang Xiang. (2002). Development and application of magnetoencephalography. China Journal of Neurosurgery Disease Research, 1(3), 3.

[8] Sun Jilin. (2005). Frequently asked questions of magnetoencephalography (meg). Journal of Modern Electrophysiology, 12(4), 5.

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