Multichannel DC current source density mapping of the Bereitschaftspotential in the supplementary and primary motor area preceding differently loaded movements

The goal of the investigation using 23 normal subjects was to clarify (1) whether the pre-movement neuronal activation in form of the Bereitschaftspotential (BF) is different e.g., in topography for different inertial loads onto a brisk finger extension, (2) if there is a difference, what kind of change is it, a global or regional one, (3) whether the early BP component (BP1) would be located in the fronto-central midline for finger extension with different loads, and (4) does the activation of the SMA occur prior to that of the primary motor area (MI). The BP preceding voluntary self-initiated extensions of the right index finger movement with different loads (low load task with 100g and high load task with 200g) was recorded on the scalp using a 64 channel DC amplifier system. The Results showed: (1) Comparison of the two tasks showed that amplitudes of the BP were significantly different in Cz and CP53. (2) The comparison of Cz with CP53 showed that the BP amplitudes were higher in Cz than in CP53 for both tasks, especially the BF1 component. (3) The comparison of the 3 motor areas (SMA, contralateral and ipsilateral MI) showed that the BP was largest in the SMA and lowest in the ipsi- MI in both tasks. (4) The CSD laplacians showed that a clear current sink (=surface negativity) of the BP appeared on the scalp as early as 2.3 sec before EMG onset. The BP2 (a late component of BF following BP1 and starting about 0.5 sec prior to movement onset, which is lateralized towards the contralateral hemisphere) current sink was lateralized in form of the contralateral preponderance of negativity (CPN). The location of the motor potential (MP) current sink was similar than that of BP2, but the areas and the densities were highest. It is concluded that the more force is needed for finger extension against load, the larger the BP in motor areas. This constitutes a regional rather than a global effect in preparation for voluntary movement. The early BP component (BP1) started in the SMA, while BP2 and the MT were laterialized in form of the CFN. The activation of the SMA occurred considerably earlier than the one of the MI.