DIPOLE SOURCE ANALYSIS SUGGESTS SELECTIVE MODULATION OF THE SUPPLEMENTARY MOTOR AREA CONTRIBUTION TO THE READINESS POTENTIAL

The readiness potential preceding voluntary movement is modulated by t he mode of movement selection, i.e. it has a higher amplitude precedin g freely selected than before prescribed movements (Praamstra, P., Ste geman, D.F, Horstink, M.W.I.M., Brunia, C.H.M. and Cools, A.R. Movemen t-related potentials preceding voluntary movement are modulated by the mode of movement selection. Exp. Brain Res., 1995, 103: 429-439). One cortical area that is likely to be involved in this modulation is the supplementary motor area (SMA). Recent attempts to elucidate the neur al generators of the readiness potential using spatiotemporal dipole s ource analysis, however, failed to establish a significant SMA contrib ution to the readiness potential. This might be explained by a failure of the proposed analyses to discriminate between SMA and motor cortex contributions to the readiness potential. We applied a dipole source analysis approach that better separates these overlapping source activ ities. The resulting source model includes an SMA source generating pr emovement activity consistent with evidence from intracranial recordin gs in humans. The SMA source accounts almost completely for the modula tion of the readiness potential by different modes of movement selecti on. On the basis of these results, the relation between scalp-recorded movement-related activity, intracranially recorded potentials, and fi ndings from functional imaging studies of voluntary movement, appears more transparent than suggested by previous dipole source analyses of premovement potentials.