Cortical Function Changes During Swallowing in Patients With Dysphagia in Lateral Medullary Syndrome

fNIRS( NirScan Danyang Huichuang Medical Equipment Co. Ltd., China) will be used to detect changes in HbO and HbR during rest and voluntary swallowing. The swallowing procedure will be used consisted of three phases of manipulations: 30-s resting state periods, 30-s swallowing periods and 30-s resting state periods. A pre-collection will be conducted before the formal collection so that the subjects could understand the test process. After the pre-collection, the subjects will take a rest for 5 minutes before the formal collection.