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Abstract:
Introduction: Mirror activity (MA) describes involuntarily occurring muscular activity in contralateral homologous limbs during unilateral movements. This phenomenon has been reported in otherwise healthy adults referred to as physiological mirror activity (pMA). According to the concept of motor overflow, pMA is hypothesized to be the result of ongoing modulation of interhemispheric communication during unilateral contractions, which leads to bilateral activation of motor-relevant brain regions (Perez & Cohen, 2008). However, it remains elusive if transcranial direct current stimulation (tDCS) of the ipsilateral motor cortex (M1) to a contracting limb is able to modulate pMA. Methods: We used a cross-over, double-blind design to apply 3 conditions (sham, anodal, cathodal) of tDCS (20 minutes, 1mA) to the ipsilateral M1 while 23 male, right-handed participants performed unilateral isometric contractions of the right hand (80%MVC) according to a block design (9 blocks, 5 x 3sec contractions per block, 5 minutes rest). Additionally, we acquired electromyography of the first dorsal interosseus muscle (FDI), bilaterally. Latency of pMA was computed as the delay between burst-onset of the actively contracting hand and the time point of elevation of muscular activity in the contralateral (resting) hand compared to its own background activity. Results: Overall, the latency of pMA decreased during the experiment. Anodal-tDCS prolonged the latency of pMA compared to sham-tDCS. Discussion: tDCS of the ipsilateral M1 is able to modulate the latency of pMA during unilateral isometric contractions in healthy adults. This result might have clinical implications for the treatment of pathological forms of MA. References: Perez, M.A. & Cohen, L.G. (2008) Mechanisms underlying functional changes in the primary motor cortex ipsilateral to an active hand. J Neurosci, 28, 5631-5640.
