Localization diagnosis of the nervous system is the determination of the site of the disease, that is, the anatomical structure. For the diagnosis of the nervous system, it includes qualitative diagnosis and localization diagnosis. For qualitative diagnosis, it is to determine the nature and cause of the disease, and for localization diagnosis, it is to determine the site of the disease. For example, if a patient has numbness and weakness of the right limb and facial numbness and weakness without dizziness or nystagmus, we first consider a lesion of the contralateral thalamus, because the thalamus is a relay station of sensation, and when it has problems, abnormalities of sensation will occur. Secondly, if the patient has dizziness, nausea, vomiting, visual rotation, nystagmus, and numbness and weakness of the limbs, we should first consider the problem of the posterior circulation, which can be a lesion of the brainstem, because the posterior circulation is in charge of balance, and when it has a lesion, the patient will experience dizziness. This is called localization diagnosis, which can usually be confirmed by MRI.