Movement-related potentials (MRPs, including Bereitschaftspotential, BP) were recorded using a 64 channel DC-EEG amplifier ("High Resolution DC-EEG", Nunez et al. 1994) in 18 subjects (Ss) to explore functions of the supplementary, the cingulate, and the primary motor area (SMA, CMA and MI). Spatial and temporal resolutions on single trials, single subject and grand average data were evaluated for preparation and execution of self-initiated index finger extensions (bilateral, right and left unilateral). Results showed that  MRPs consisted of six waves: Early component (BP1) of the MRPs, late component (BP2) of the MRPs, Motor potential (MP), Post movement positive potential (PMPP), Movement-evoked potential I (MEP I) and Movement-evoked potential II (MEP II).  Onset of BP1 was earliest in the mesial wall motor areas, SMA/CMA, then in the contralateral MI (conMI) and latest in the ipsilateral MI (ipsMI).  MRP amplitudes were maximum in the SMA/CMA in all three tasks. In the unilateral tasks, MRP amplitudes were higher in the conMI than they were in the ipsMI.  The early BP component (BP1) was always localized in the fronto-central midline (overlying the mesial wall motor areas SMA and CMA). BP2, MP, PMPP, MEP1 and MEP II showed clear lateralized distributions (contralaterally larger) for unilateral movement but not for bilateral movement.  BP2, MP, PMPP, MEPI and MEPII in bilateral movement are not just the mathematical sum of right and left unilateral movements on both hemispheres.  The three tasks influenced all six MRP components.  Current source density maps, which were relatively robust between different tasks, further demonstrated that BP1 stemmed from the fronto-central midline (mesial wall motor areas).  MANOVA showed that there were several statistically significant differences (p<0.001) across the multiple combinations between time points of the epoch (20), electrodes (56) and tasks (3).
Conclusions:  SMA/CMA participates in preparation and initiation of volitional index finger extensions, while MI participates in their execution and performance.  BP1 stems primarily from the mesial wall motor areas, SMA and CMA.  SMA/CMA subserves the temporal organization of sequential movements and bimanual coordination.