Differential after-effects of bimanual activity on mirror movements

Using a rhythmic isometric force production paradigm, we investigated the after-effects of in-phase and antiphase bimanual performance on the unintended recruitment of the homologous muscles of the opposite limb during subsequent performance of tasks that were unimanual by design. Electromyograms obtained from the muscles of the opposite limb were analyzed in terms of their amplitude and the distribution of their phase relative to that of the intended movements. Preceding bimanual activity had distinct effects on the relative phase (mean and uniformity) of the structured electromyograms. These were particularly pronounced following performance of the in-phase pattern. These findings are discussed in terms of interhemispheric excitation and inhibition.