Movement-Related Potentials and Magnetic Fields: New Evidence for SMA Activation Leading MI Activation Prior to Voluntary Movement

Abstract

Movement is the essence of life. Without movement one cannotachieve anything. Consequently, during evolution, movement has been optimized to highest levels of precision. Visible sign of the evolution of movement is that more and more brain has been assigned for motor purposes. A carnivore´s motor cortex is just a `dimple' in its brain supported by merely a minimal frontal cortex. In the primate, the dimple evolved into a motor strip and shifted from an anterior to a central position, in order to accommodate more and more frontal brain. Homo sapiens neanderthalensis with his sloping forehead still had less frontal cortex than Homo sapiens sapiens. In the latter, about half the cortex is pre-rolandic, assigned to motor purposes in the broader sense, i.e. including areas that supply to motor such as premotor, prefrontal, etc. areas. These frontal supplier areas to motor are involved in functions such as motivation, preparation, volition, will, planning, foresight, active anticipation, precaution, intent to act, purposefulness, goal-directedness, etc. i.e. all these functions are frontal in location, and the function of the frontal lobes seems to be almost entirely behavour-related including - in man - all the future-related behavioural aspects. A special role may be assigned to the frontomesial cortex including the supplementary motor area (SMA) and the cingulate motor area (CMA). The brain apparatus supporting motor is among the most recent and highly organized cerebral structures (neoneocortex), and the corticalization of movement developed in a saltatory way in primate phylogenesis. There are many movements man can perform, but basically there are only two primordial categories of movements: Self-initiated voluntary movements = actions and responsive (externally triggered) movements = re-actions. The first category is preceded by a Bereitschaftspotential, the latter occurs between S1 and S2 of a re-action paradigm (Walter et al. 1964). Regarding the BP, recent evidence using multichannel (64) DC-EEG (time constant [tau] = [infinity]) computer-assisted amplification proved that the earliest activity occuring is over the SMA/CMA. Only later comes the primary motor area (MI) into play. This was also shown using current source density techniques (laplacians with spline interpolation), multichannel (143) MEG and FMRI.