Intracranial tumors located in and near functional areas are prone to functional impairment with surgical treatment, such as hemiparesis, limb sensory impairment, and aphasia. To achieve adequate tumor removal while better protecting important neurological functions, the first step is to achieve functional brain area localization. The methods of brain functional area localization include preoperative localization and intraoperative localization. The former mainly includes imaging anatomical localization, functional magnetic resonance imaging (fMRI) localization and magnetoencephalography (MEG) localization, while the latter is mainly intraoperative neurophysiological monitoring (IOM). Conventional preoperative functional area localization is judged based on imaging anatomy. When the tumor is located in or near the functional area, the anatomical structure is displaced and indistinguishable due to factors such as lesion pushing and tissue edema; some patients may also have the phenomenon of functional area remodeling, which makes it difficult to complete functional localization according to the anatomical structure. In this group of cases, MEG was chosen to localize the functional brain area. 1. principle and application of magnetoencephalography. meg records the physiological changes of brain magnetic field in real time. In the early 1990s, whole-head magnetoencephalography began to be used in clinical practice, which can record the whole-brain magnetic signal synchronously at one time, then calculate the localization of activated cells according to certain mathematical models, fuse the corresponding positions in MRI images, and obtain the image localization of functional brain areas. Currently, the main brain evoked magnetic field techniques are somatosensory evoked magnetic field (SEF), motor evoked magnetic field (MEF), auditory evoked magnetic field (AEF), and visual evoked magnetic field (VEF). field (AEF) and visual evoked magnetic field (MEF). In our group of 24 patients, a combination of these methods was used to obtain functional area localization. The surgical results showed that the localization was accurate and the efficacy was satisfactory. 2. The relationship between tumor and functional area and the principle of surgery. From the analysis of the localization results of this group, there are two categories: (1) Nudging: The tumor is adjacent to the functional area or has no direct relationship with it, but only squeezes and pushes the surrounding brain tissue because of the occupancy effect. It is further divided into two categories: extra-cortical and sub-cortical. Extra-cortical, such as dorsolateral cerebral hemispheres and parsagittal meningiomas, metastases, etc., follow the principle of minimally invasive operation in micro-neurosurgery during surgery, and the possibility of neurological function damage is low. Subcortical, on the other hand, it is necessary to choose the appropriate surgical access according to the functional localization, avoiding the functional area shown by MEG, usually choosing its anterior or posterior cerebral sulcus for entry. (2) Infiltration: The tumor infiltrates between normal brain tissues, and the presence of normal neurons and nerve fibers within the tumor shown by imaging makes it difficult to distinguish and protect morphologically. the MEG localization results show that it is subdivided into two types, partially located within the functional area and completely located in the functional area. In our group, MEG recorded the activity of functional areas within the tumor in 33% of patients, all of whom were low-grade gliomas (WHO grade II). Four patients with glioma in our group were completely located in the functional area, and although they were subtotal resected tumors, they still showed irreversible neurological dysfunction, which showed the presence of functional neural tissue within the tumor. Therefore, its localization result is an important reference index for physicians to assess the extent of tumor resection and functional protection preoperatively, and to predict the feasibility of surgical resection and the neurological function status of patients after surgery. In cases where the tumor significantly infiltrates into the functional area of the brain, perhaps surgery should be abandoned; while those with partial infiltration need to preserve the part of tissue where function exists. 3. The effect of the nature of the tumor on the functional area. The nature of the tumor determines the relationship between the tumor and the functional area. For example, meningioma and metastasis are mainly swelling growth and mostly infiltrate to functional areas; while tumors of neuroepithelial tissue origin such as glioma are mainly infiltrating growth and mostly infiltrate to functional areas. In our four cases, no neurological activity was seen inside the glioma with high malignancy (WHO grade III and IV), which may be due to the following reasons: (1) fast growth rate, mainly swelling growth in the form of masses; (2) obvious destruction of normal tissues and loss of their functions. 4. The localization of functional areas of the magnetoencephalography is combined with the neuronavigation system. Neuronavigation can accurately localize positive lesions in any part of the brain. Usually the neuronavigation system uses CT and MRI images to locate organic positive lesions. When the whole brain functional area is localized and labeled by magnetoencephalography, the neuronavigation can indicate the functional area as a positive target in real time. Marking the location of brain tumor and important functional areas under navigation guidance during surgery can protect the functional areas more accurately. Since the navigation workstation images are not real-time images, the relative displacement of brain tissue during the application may reduce the accuracy of the navigation, and our group adopted the “fence method” to avoid the errors caused by the displacement of brain tissue. (1) Navigation-assisted design of the surgical incision, planning of the surgical approach, and protection of the functional cortex during resection of subcortical tumors; (2) Intraoperative real-time positioning, clarifying the location of the tumor and functional area, and suggesting the relationship between them, further improving surgical safety while fully removing the tumor. 5. Superiority of MEG functional positioning. Other commonly used functional localization methods include functional magnetic resonance imaging (fMRI) and intraoperative cortical electrical stimulation. fMRI uses blood oxygenation level dependent BOLD method signal detection, which varies significantly among individuals, and the application of absolute stimulation threshold is not credible. When subjected to external stimulation, fMRI can integrate brain activity over several seconds, demonstrating that the entire cortical network is involved in this activity. The limited discrimination in the temporal domain may cause difficulties in distinguishing primary areas of interest from secondary processing areas; fMRI activation in non-primary areas may also confound the interpretation of active areas. This problem is effectively avoided by the millisecond interpretation of cortical activity by MEG, which allows the discrimination of primary somatosensory cortices from secondary activity. Intraoperative electrical cortical stimulation is often used to localize functional areas intraoperatively. Due to the method of localization, there are errors in the localization of cortical stimulation, and Schiffbauer et al. observed a spatial variation of 11 ± 1 mm for the same source of response to cortical excitation. Other shortcomings are: (1) preoperative planning, such as surgical access design, is not possible; (2) a large bone flap craniotomy is required; (3) intraoperative arousal is partially required, requiring a high degree of patient cooperation, which can easily induce adverse outcomes. MEG is a direct recording of magnetic field generated by intracellular electrical activity with 1ms temporal resolution and 2mm spatial resolution.MEG functional localization is a preoperative non-invasive functional localization technique, which can locate important functional areas of human brain more accurately, clarify the relationship between tumor and functional area location, and locate and remove tumor under the guidance of neuronavigation system, which is an important guidance for tumor surgery in and around functional areas and can It can reduce the occurrence of neurological dysfunction and improve patients’ postoperative quality of life.