Propriospinal cutaneous-induced EMG suppression is unaltered by anodal tDCS of healthy motor cortex

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Journal Article
Clinical Neurophysiology, 2017, 128 (9), pp. 1608 - 1616
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© 2017 International Federation of Clinical Neurophysiology Objective Cervical propriospinal premotoneurons (PN) relay descending motor commands and integrate peripheral afferent feedback. Effects of anodal transcranial direct current stimulation (a-tDCS) on propriospinal excitability in the upper limbs are unknown. Methods Healthy right-handed adults received a-tDCS or sham tDCS over primary motor cortex (M1) at 1 mA (Experiment 1, n = 18) or 2 mA current intensity (Experiment 2, n = 15). Propriospinal excitability was assessed by suppression of background electromyography (EMG) in extensor carpi radialis (ECR) from electrical stimulation of the superficial radial nerve during bilateral (Experiment 1 and 2) or unilateral (Experiment 2 only) activation of the left and/or right ECR. EMG suppression could be attributed to an early propriospinal component and late cortical component. Motor evoked potentials (MEP) were obtained as a manipulation check. Results Before tDCS, propriospinal-mediated cutaneous-induced suppression was present in each arm for early and late components. ECR MEP amplitude increased after 1 mA, but not 2 mA, a-tDCS. Neither 1 mA nor 2 mA a-tDCS modulated either component of ipsilateral or contralateral propriospinal excitability during bilateral or unilateral tasks. Conclusions Propriospinal-mediated cutaneous-induced suppression was not modulated by a-tDCS in healthy adults. Significance Reporting non-significant findings is paramount for the development of clinically-relevant tDCS protocols.
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