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Modulation of intermuscular coherence between homologous muscles reflects different common neural drive regulating bilateral contractions

Abstract : Objectives In healthy adults, homologous muscle activations appear during bilateral contractions (BI) and can be induced during unilateral contractions (UNI) at high force level. After brain injury, involuntary homologous muscle activations during UNI can have neurological significance. Although homologous muscle activations are supposed to originate from commands sent by the motor cortices [1], the common neural drive shared across homologous muscles remains unclear. The intermuscular coherence (IMC) between electromyographic (EMG) signals can highlight different neural strategies to control muscle activations [2, 3]. The IMC∼10Hz is supposed to reflect subcortical strategies while IMC in higher frequency bands is supposed to reflect different cortical contributions. This study compared the IMC between homologous muscles according to contraction type. Methods Eleven right-footed subjects performed 3 maximal isometric UNI and BI ankle plantarflexion contractions. Right and left ankle torque and homologous triceps surae EMG signals were recorded. IMC magnitude between homologous EMG signals was calculated in α (5–12Hz), β (13–30Hz), γ (30–60Hz) and γ+ (>60Hz) frequency bands during the 2s where the net ankle torque was maximal. Right and left torques and IMC magnitudes were compared between UNI and BI. Results Right torque was not significantly different between conditions. Left torque was significantly different from baseline and between conditions. IMCα was significantly higher during UNI than BI. No significant differences in IMCβ and IMCγ between conditions were observed. IMCγ+ was significantly higher during BI than UNI. Conclusions Our results suggest different neural strategies to control muscle activations according to contraction type. During UNI, higher IMCα suggests subcortical structures involvement to inhibit unsolicited homologous muscle activations [3]. During BI, higher IMCγ+ may suggest an optimization of the neural drive shared across homologous muscles to reduce computational effort [2, 3]. Similar investigations in people with brain injury may help understanding the underlying neurophysiological mechanisms of motor overflow.
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Submitted on : Thursday, December 2, 2021 - 10:52:49 AM
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Emilie Mathieu, Gauthier Desmyttere, Emilie Simoneau-Buessinger, Sylvain Cremoux. Modulation of intermuscular coherence between homologous muscles reflects different common neural drive regulating bilateral contractions. 3èmes Journées de Neurophysiologie Clinique (JNC), Jun 2018, Lille, France. ⟨hal-03462964⟩

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