Movement-related cortical d.c. shifts accompanying the execution of four different prehensile tasks were investigated using six normal adult subjects. The goal was to identify patterns of brain electrical activity that differentiated a precision grip configuration (thumb and index finger or 2f) from a full precision grip configuration (thumb and all fingers or 5f) at different total force levels. As such, this was the first study to systematically manipulate both grip configuration and force level while also measuring movement-related potentials (MRP) during the control phase of an isometric prehensile task. This investigation focused on assessing the sustained, performance-related negativity (N-P) associated with the execution of particular grip configurations at different total force levels (percentage maximum voluntary force, MVF). The results from this study demonstrated significant interactions between grip configuration, force level and amplitude of the N-P. First, an overall increase in force output does not correspond to larger N-P amplitudes under these task conditions. Second, force level and grip configuration interact significantly in determining the peak N-P, especially in low-force conditions. Overall, the findings reveal a task-specific sensitivity of movement-related potentials associated with the control phase of a prehensile force task while humans execute different grip configurations and force levels.
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