Event-related desynchronization (ERD) 2.0 sec before and 1.0 sec after movement in the frequency bands of 8-10, 10-12, 12-20 and 20-30 Hz and movement-related cortical potentials (MRCPs) to self-paced movements were studied from subdural recordings over the central region in 3 patients, and from scalp-recorded EEGs in 20 normal volunteers. In direct cortical recordings, the peak ERD response and peak MRCP amplitude to self-paced finger movements were maximal over recording sites in the contralateral hand motor representations. The topography and time of onset of the ERD response to finger and foot movements suggest that the ERD responses in the 8-10 Hz and 10-12 Hz bands are more somatotopically restricted than the responses in the higher frequency bands. The power recovery and subsequent overshoot in the different frequency bands occurred in an orderly fashion with the faster frequencies recovering earlier. The ERD responses on the scalp-recorded EEGs were of lower magnitude and more widely distributed than those occurring on the subdural recordings. Across the population, there was no relation between the magnitude of the ERD response in any of the frequency bands studied and the peak amplitude of the negative slope (pNS') and the frontal peak of the motor potential (fpMP) of the MRCPs. MRCPs and ERD responses originate in similar cortical regions and share some common timing features, but the magnitude and spatial distribution of the two responses appear to be independent of each other, which suggests that the physiological mechanisms governing these two events are different and may represent different aspects of motor cortex activation. Differences in the timing and topographical features of the ERD responses in the various frequency bands also suggest a distinct functional significance for the various spectral components of the electrical activity in the motor cortex.