Bimodel Control of Fast Forearm Movements through Central Commands

Abstract

In this paper we analyze relations among the waveforms and the electromyograms (EMGs) of fast, or ballistic, movements of the forearm and propose a concept of the bimodal control policy of the motor center. The central commands described as change of impulse density in motor nerves are extracted from the EMGs on the basis that the ballistic portion of fast movements is solely under open loop control. Of the several parameters analyzed the amplitude of the agonist and antagonist commands and the time difference between the both command onsets closely correlate with the acceleration waveforms and they are suggested to be the essential central parameters that control the ballistic movements. In relatively small movements the command amplitude varies according to the movement amplitude while the onset time difference is kept rather constant. On the other hand, in larger movements the former takes the extremum value and the latter increases in proportion to the movement amplitude. These two exclusive ways of movement control are rational from the standpoint of attainment of high speed and accuracy of voluntary movements.