In a number of recent studies, the specific sensitivity of movement-related EEG potentials toward experimental manipulations of motor tasks using the index finger as a primary end-effector is well documented. The major question in this study was whether different movement-related EEG components are primarily end-effector or task dependent. Accordingly, the experimental task (i.e., the rate of force development a ratio of peak force to time-to-peak force) was systematically manipulated and the effects of this manipulation on movement-related potentials were examined while subjects used either the index, middle, ring or little finger. Significant effects observed in this study were due mainly to the sensitivity of movement-related potentials preceding movement onset (Bereitshaftspotential and motor potential) toward the specific finger performing the task and the sensitivity of components accompanying the task (movement-monitoring potential) toward the rate of force development. In addition, both movement-related potentials preceding and accompanying movement significantly changed as a function of the finger performing the slow task (lower rate of force development) with maximum values observed for the ring finger and minimal values observed for the index finger. Behaviorally subjects were less accurate during slow tasks regardless of the finger performing the task. In contrast, the amplitude of neither early nor late components of movement-related potentials changed as a function of the finger performing the fast task (higher rate of force development). Overall, our results are consistent with the notion that the whole complex of movement-related EEG potentials reflect a combination of factors including the selection of corresponding general motor programs as reflected in the amplitude of potentials preceding movement and specific elements of the task including rate of force development as reflected in the amplitude of potentials accompanying movement execution.
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