| Previous research suggests that cellular activity in primary motor cortex is related to the rate of force development (dF/dt) and Peak Force (PF). A series of four studies that investigate this relationship in humans performing a handgrip task under various feedback conditions and recording methodologies are reported.; The first experiment compared the fMRI BOLD signal at three levels of sustained isometric handgrip force and a dynamic finger task. Signal intensity was found to be relatively constant across all tasks, while the area of activation increased as a function of force, and was greatest for the dynamic task.; Slobounov et al. (1998) reported that Movement-Related Potentials (MRPs) associated with a finger force-production task reflect dF/dt, but not PF. Continuous visual feedback (CFB) allowed their subjects to visually track force output, potentially confounding the interpretation of MRP changes. Thus, the second experiment was carried out to determine whether subjects could generate target force-time trajectories in the absence of CFB. Subjects receiving CFB were more accurate in all force parameters than subjects receiving terminal visual feedback (TFB). In a subsequent no-feedback retention task, the subjects trained with CFB showed little evidence of learning the target dF/dt.; The third experiment compared the Movement-Related Potentials (MRPs) of subjects generating target time-force trajectories with CFB or TFB. Only under conditions of CFB was there a significant relationship between negativity of the Movement Related Potentials (MRPs) and dF/dt. However, the TFB condition in this experiment was not completely effective in eliminating task-related eye movements. The final experiment investigated the effects of variations in dF/dt and peak force levels on MRPs during a task that further reduced task-related eye movements by requiring subjects to visually fixate a static cue signal during the production of target force-time trajectories. Although an unexpected positive potential (P300) partially masked the typical slow wave negative potentials associated with movement preparation and termination, no relationship was found between dF/dt and the MRP negativity during movement. |
