Feedback-dependent modulation of isometric force control: An EEG study in visuomotor integration

The primary purpose of this investigation was to examine the cortical mechanisms underlying visuomotor integration in an experiment directly manipulating visual feedback (control-signal gain) as participants executed a grasping task. This was accomplished by assessing human electroencephalograms in both time and frequency domains and relating these measures to the performance accuracy of isometric force control. The basic experimental manipulation consisted of subjects controlling a grip dynamometer and the subsequent force trace displayed on a computer monitor at various magnitudes of force output and control-signal gain. Several findings from this study were of interest. First, the effects of control-signal gain and its interplay with the magnitude of force were most evident across the parietal and frontocentral electrode locations - areas specifically related to multi-modal sensory evaluation (parietal lobe) and higher-order movement control (supplementary and mesial premotor areas). Second, electroencephalography (EEG) measures in the time domain, i.e., slow-wave potentials, were sensitive to control-signal gain only during the ramp phase of force production (period of reaching the target force), not the static phase (period of maintaining the target force level). Third, EEG measures within the frequency domain (event-related desynchronization), unlike the slow-wave potential measures, were sensitive to control-signal gain during the static phase of force production - a sensitivity that was directly related to improvements in the accuracy of isometric force control. The findings of this investigation are described in relation to the existent literature on human visuomotor integration with special attention paid to the distinct spatial and temporal electrocortical patterns exhibited under varying degrees of visual feedback and magnitudes of force output during grasping.