In a brain-computer interface, using event-related desynchronization and synchronization(ERD and ERS), intuitive command input is available. Switching precision was thought to be improved by a detailed examination of the ERD ���� rhythm in the time-frequency domain. In the experiment, measured electroencephalograms of motor cortex in the resting state, hand grasp motion, and hand grasp recall were analyzed. Consequently, desynchronization was observed in the band centered at 12 Hz for both the grasp motion and grasp recall.