Inclusion Criteria:  Adult patients who aged 20-70 years with ASA-PS 1-3, diagnosed of ossification of the posterior longitudinal ligament or cervical spondylotic myelopathy, in need of intraoperative neurophysiological monitoring  Exclusion Criteria:  Tolerance or hypersensitivity to benzodiazepine or propofol Dependence or addiction to psychotropic drugs or alcohol Previous brain-related neurosurgery Inserted status of pacemaker Inserted status of intracranial device Steroids use during surgery Pregnant women, subjects who lack the ability to make decisions and susceptible to voluntary participation decisions