EEG is a test that uses an EEG machine to magnify the bioelectricity of the brain cells working to produce a weak electric current several million times, and then records the undulation curve on paper. By placing multiple electrode plates on the patient’s head, this current increase is captured and the potential difference is traced as a waveform to understand whether there are any abnormalities in brain function. In cases of epilepsy, brain tumors, cerebral infarction, traumatic brain injury, etc., a waveform specific to each of these conditions will appear, which is not present in healthy people. Therefore, this test can diagnose which part of the body has a disease. In addition, it is also valuable for diagnosing insomnia and dementia. Epilepsy: EEG is the most meaningful test for diagnosing epilepsy. EEG can accurately record special waveforms during seizures, such as scattered slow waves, spikes or irregular spikes, so it is very accurate for diagnosing epilepsy, and EEG has a guiding effect on the discontinuation of antiepileptic drugs. Psychiatric disorders: For the diagnosis of schizophrenia, manic-depressive disorder and other psychiatric abnormalities, EEG can be done to exclude other disorders of the brain including epilepsy. Other diseases: The patterns of brain activity traced by EEG can not only indicate the limited or diffuse pathological manifestations caused by diseases of the brain itself, such as epilepsy, tumors, trauma and degenerative diseases, but also have some diagnostic value for changes in the central nervous system caused by extracerebral diseases, such as metabolic disorders and poisoning. Therefore, EEG is an effective method to examine changes in brain function. Since changes in brain function are dynamic and variable, patients who do not find abnormalities in one EEG examination cannot completely exclude the existence of brain diseases, but should have regular EEG reexamination to detect diseases more accurately.