An examination of brain waves, clinically known as an electroencephalogram (EEG). EEG can reflect the electrical signals generated by neuronal activity and is generally used to detect the functional state of the cerebral cortex. EEG is mainly used to determine the site of lesions, diagnosis and differential diagnosis of brain diseases, etc. It can be used to check encephalitis, toxic encephalopathy, epileptic seizures, traumatic brain injury and so on. 1. Diffuse cerebral cortex lesions: when there are diseases such as hypoxic encephalopathy, encephalitis, drug poisoning, etc., diffuse slow wave changes can be detected on EEG. 2. Focal lesions: If the patient has seizures, the EEG can detect epileptiform discharges, such as spikes, sharp waves, spike slow waves, etc. Therefore, the EEG can be used for epilepsy examination. In addition, brain abscess, focal subdural hematoma, etc. can show focal slow wave on EEG. 3. Other abnormal lesions: when the patient has Creutzfeldt-Jakob disease, the EEG may show triphasic waves, and EEG can also be used for the diagnosis of these diseases. EEG is an auxiliary examination. The diagnosis of the disease should be considered together with the patient’s symptoms and signs, age of onset and other auxiliary examinations.