The causes of left brain pain are as follows: 1. For example, if there is an occupational lesion in the left side of the brain, the patient may have headache and nausea due to local edema caused by the occupational lesion, which is mainly on the left side; 3, then there are some large cerebral infarcts, such as occlusion of the middle cerebral artery on the left side, the patient may have infarction of the left cerebral hemisphere, and the patient may have left-sided headache and unfavorable movement of the right limb; 4, then there are some intracranial infectious diseases, such as encephalitis or meningitis, which are mainly on the left side. Meningitis is predominantly left-sided, and the patient can also have left-sided headache or full headache, accompanied by nausea and vomiting.