SUPPLEMENTARY MOTOR AREA IN SPATIAL COORDINATION OF BILATERAL MOVEMENTS - A NEW ASPECT TO THE SMA DEBATE

To test whether the supplementary motor area's (SMA) role is confined to determining the 'temporal' but not the 'spatial' properties of a mo vement (H.H. Komhuber et al., in: W.A. Hershberger (Ed.), Volitional A ction. Elsevier, Amsterdam, 1989, pp. 107-168), movement-related scalp -recorded negative DC potential shifts were recorded in bilateral move ments requiring complex spatial coordination. In such bilateral contin uous rotation movements, the effect of the rotation sense (symmetrical vs. antisymmetrical), i.e. the direction in which an arm or a finger rotated in relation to the other, heavily affected DC shifts over the frontocentral midline. Antisymmetrical rotation of upper Limb segments was associated with higher negative DC shifts than symmetrical rotati on was. This was true for rotations in the sagittal plane, irrespectiv e of whether the rotation involved predominantly proximal muscles (by a rotation predominantly in the shoulder) or only distal muscles (by a rotation in the metacarpo-phalangeal joint of the index finger). If t hese negative cortical DC-shifts over the frontocentral midline relate to activity of mesial frontocentral structures including the SMA, the n the present results suggest that there is a role for these cerebral areas in spatial coordination of bilateral movements. Surprisingly, th is was not the case for similar finger movements performed in the fron tal plane. The results of the present study and particularly the consi dering of some fundamentals of theoretical physics and of Popper's phi losophy of science, made us revise our assumption motivating the prese nt study, that time and space would represent two orthogonal factors o f a movement and that the contributions of a particular cerebral motor area (such as the SMA) to 'spatial parameters' versus 'temporal param eters' of a movement can thus be teased apart. Copyright (C) 1996 Else vier Science Ireland Ltd.