EVENT-RELATED DESYNCHRONIZATION AND MOVEMENT-RELATED CORTICAL POTENTIALS ON THE ECOG AND EEG

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 an d movement-related cortical potentials (MRCPs) to self-paced movements were studied from subdural recordings over the central region in 3 pa tients, and from scalp-recorded EEGs in 20 normal volunteers. In direc t cortical recordings, the peak ERD response and peak MRCP amplitude t o 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 th e ERD responses in the 8-10 Hz and 10-12 Hz bands are more somatotopic ally restricted than the responses in the higher frequency hands. The power recovery and subsequent overshoot in the different frequency ban ds occurred in an orderly fashion with the faster frequencies recoveri ng earlier. The ERD responses on the scalp-recorded EEGs were of lower magnitude and more widely distributed than those occurring on the sub dural recordings. Across the population, there was no relation between the magnitude of the ERD response in any of the frequency bands studi ed and the peak amplitude of the negative slope (pNS') and the frontal peak of the motor potential (fpMP) of the MRCPs. MRCPs and ERD respon ses originate in similar cortical regions and share some common timing features, but the magnitude and spatial distribution of the two respo nses appear to be independent of each other, which suggests that the p hysiological mechanisms governing these two events are different and m ay 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 significanc e for the various spectral components of the electrical activity in th e motor cortex.