Abstract
Pathways of the human mirror neuron system are activated during both, action observation and action execution, including lateralized activation of respective areas, as shown by observed right-or left-hand actions. Here, we investigated whether execution-dependent motor cortex excitability is affected by prior interaction between transcranial random noise stimulation (tRNS) and action observation. Sham or real tRNS (1 mA) was applied for 10-min over the left primary motor cortex during action observation. In the main experiments, participants received sham or real tRNS while they watched a video showing repeated tapping tasks, involving either the right-hand (Experiment 1, congruent action observation), or a mirror-reversed video showing the same performance (Experiment 2), followed by action execution of the right-hand. In control Experiments 1–3, participants received real tRNS while observing a perceptual sequence, watching a landscape picture, or observing the left-hand performing the action (the sequence was identical to Experiment 1), followed by action execution of the right-hand. In control Experiment 4, participants received real tRNS during congruent action observation, and then took 6-min rest. Motor-evoked potentials (MEP) were recorded before action observation, a perceptual sequence or a landscape picture, immediately after, and after action execution, or an interval of 6-min, dependent on the respective experimental condition. MEPs in the right first dorsal interosseous muscle increased significantly after real tRNS combined with congruent action observation, and after action execution compared to the sham session in Experiment 1 and control experiments. We conclude that prior interaction between real tRNS and action observation of mirror-matched movements modulates subsequent execution-dependent motor cortex excitability.
Highlights
Motor cortical activity can be modified by observing others perform a matching movement known as observational learning, occurring for both explicitly and implicitly acquired motor skills (Heyes and Foster, 2002)
To clarify specificity of these effects further, in the third experiment, we explored if (1) real transcranial random noise stimulation (tRNS) combined with observation of a perceptual sequence, or a landscape image, followed by action execution; (2) real tRNS combined with action observation, in which the observed tapping posture is incongruent with the subsequent motor performance, and (3) real tRNS combined with action observation, but not followed by actively executed movements does induce similar alterations of motor cortex excitability to those obtained in Experiment 1
In the fourth control experiment, we explored whether real tRNS combined with action observation, but without action execution, promotes similar cortical excitability alterations as those obtained in Experiment 1
Summary
Motor cortical activity can be modified by observing others perform a matching movement known as observational learning, occurring for both explicitly and implicitly acquired motor skills (Heyes and Foster, 2002). The underlying mirror mechanisms result in comparable activation of motor or motor-related cortical networks when individuals are observing or conducting the identical action (Mattar and Gribble, 2005; Loporto et al, 2011). This neural system activation by observation enhances motor skill acquisition of the observer (Heyes and Foster, 2002; Nielsen and Cohen, 2008). Action observation training is increasingly used for promoting motor learning processes in humans (Mattar and Gribble, 2005; Stefan et al, 2005; Loporto et al, 2011), including its application as treatment modality in motor rehabilitation (Ertelt et al, 2007; Bisio et al, 2017; Zhang et al, 2018)
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