EEG abnormalities are caused by various functional or organic damage to the brain. Functional damage does not have MRI or CT imaging abnormalities and is triggered by various triggers, such as prolonged sleeplessness, late nights, and mental overwork. Organic causes are better understood, such as various types of encephalitis, cerebrovascular disease, brain tumors, brain parasitic diseases, and any disease that can cause brain damage may cause EEG abnormalities. The most common diseases that can cause cortical lesions are encephalitis and meningitis, with viral encephalitis and viral meningitis being the main representatives. Viral encephalitis mostly involves the temporal lobe and frontal lobe, and may result in mental disorders and seizures, and the EEG often has seizure waves in addition to increased slow waves.