Supplementary motor area activation preceding voluntary movement is detectable with a whole-scalp magnetoencephalography system

Despite the fact that the knowledge about the structure and the function of the supplementary motor area (SIMA) is steadily increasing, the role of th e SMA in the human brain, e,g., the contribution of the SMA to the Bereitsc haftspotential, still remains unclear and controversial. The goal of this s tudy was to contribute further to this discussion by taking advantage of th e increased spatial information of a whole-scalp magnetoencephalography (ME G) system enabling us to record the magnetic equivalent of the Bereitschaft spotential 1, the Bereitschaftsfeld 1 (BF 1) or readiness field 1, Five sub jects performed a complex, and one subject a simple, finger-tapping task. I t was possible to record the BF 1 for all subjects. The first appearance of the BF 1 was in the range of -1.9 to -1.7 s prior to movement onset, excep t for the subject performing the simple task (-1 s). Analysis of the develo pment of the magnetic field distribution and the channel waveforms showed t he beginning of the Bereitschaftsfeld 2 (BF 2) or readiness field 2 at abou t -0.5 s prior to movement onset. In the time range of BF 1, dipole source analysis localized the source in the SIMA only, whereas dipole source analy sis containing also the time range of BF 2 resulted in dipole models, inclu ding dipoles in the primary motor area. In summary, with a whole-head MEG s ystem, it was possible for the first time to detect SMA activity in healthy subjects with MEG. (C) 2000 Academic Press.