Abstract
We investigated differences in corticospinal and spinal control between discrete and rhythmic ankle movements. Motor evoked potentials (MEPs) in the tibialis anterior and soleus muscles and soleus H-reflex were elicited in the middle of the plantar flexion phase during discrete ankle movement or in the initial or later cycles of rhythmic ankle movement. The H-reflex was evoked at an intensity eliciting a small M-wave and MEPs were elicited at an intensity of 1.2 times the motor threshold of the soleus MEPs. Only trials in which background EMG level, ankle angle, and ankle velocity were similar among the movement conditions were included for data analysis. In addition, only trials with a similar M-wave were included for data analysis in the experiment evoking H-reflexes. Results showed that H reflex and MEP amplitudes in the soleus muscle during discrete movement were not significantly different from those during rhythmic movement. MEP amplitude in the tibialis anterior muscle during the later cycles of rhythmic movement was significantly larger than that during the initial cycle of the rhythmic movement or during discrete movement. Higher corticospinal excitability in the tibialis anterior muscle during the later cycles of rhythmic movement may reflect changes in corticospinal control from the initial cycle to the later cycles of rhythmic movement.
Highlights
Rhythmic movement has been said to be under a unique control mechanism: it is produced by the subcortical rhythm generator system in mammalians (Brown, 1911; see the reviews by Duysens and Van de Crommert, 1998; Guertin, 2009)
Another study found that soleus (SOL) Hreflex was depressed during late downstroke while bicycling and motor evoked potential (MEP) in the SOL muscle was facilitated during early downstroke compared with those during tonic plantar flexion (Pyndt and Nielsen, 2003)
H-reflex was evoked in Section “Experiment 1,” and MEP was evoked in Section “Experiment 2.”
Summary
Rhythmic movement has been said to be under a unique control mechanism: it is produced by the subcortical rhythm generator system in mammalians (Brown, 1911; see the reviews by Duysens and Van de Crommert, 1998; Guertin, 2009). In humans some evidence for the involvement of the subcortical rhythm generator system for controlling rhythmic movement has been found (Bussel et al, 1978; Dimitrijevic et al, 1998). In order to elucidate this mechanism, corticospinal or spinal control of rhythmic movement has been typically compared with the control of tonic contraction in humans. The excitability of the corticospinal pathway, H-reflex, and the fast monosynaptic corticomotoneuronal pathway in the flexor carpi radialis muscle during rhythmic arm cycling has been found to be lower than during tonic contraction (Carroll et al, 2006). Corticospinal and/or spinal control during rhythmic movement may be different from that during tonic contraction
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