New evidence of corticospinal network modulation induced by motor imagery

Motor imagery (MI) is the mental simulation of movement, without the corresponding muscle contraction. Whereas the activation of cortical motor areas during MI is established, the involvement of spinal structures is still under debate. We used original and complementary techniques to probe the influ...

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Bibliographic Details
Published in:Journal of neurophysiology 2016-03, Vol.115 (3), p.1279-1288
Main Authors: Grosprêtre, Sidney, Lebon, Florent, Papaxanthis, Charalambos, Martin, Alain
Format: Article
Language:English
Subjects:
Bioinformatics
Computer Science
Evoked Potentials, Motor
H-Reflex
Humans
Imagination
Life Sciences
Male
Motor Cortex - physiology
Muscle Contraction
Muscle, Skeletal - innervation
Muscle, Skeletal - physiology
Neural Circuits
Neurons and Cognition
Psychomotor Performance
Pyramidal Tracts - physiology
Young Adult
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Summary:Motor imagery (MI) is the mental simulation of movement, without the corresponding muscle contraction. Whereas the activation of cortical motor areas during MI is established, the involvement of spinal structures is still under debate. We used original and complementary techniques to probe the influence of MI on spinal structures. Amplitude of motor-evoked potentials (MEPs), cervico-medullary-evoked potentials (CMEPs), and Hoffmann (H)-reflexes of the flexor carpi radialis (FCR) muscle and of the triceps surae muscles was measured in young, healthy subjects at rest and during MI. Participants were asked to imagine maximal voluntary contraction of the wrist and ankle, while the targeted limb was fixed (static condition). We confirmed previous studies with an increase of FCR MEPs during MI compared with rest. Interestingly, CMEPs, but not H-reflexes, also increased during MI, revealing a possible activation of subcortical structures. Then, to investigate the effect of MI on the spinal network, we used two techniques: 1) passive lengthening of the targeted muscle via an isokinetic dynamometer and 2) conditioning of H-reflexes with stimulation of the antagonistic nerve. Both techniques activate spinal inhibitory presynaptic circuitry, reducing the H-reflex amplitude at rest. In contrast, no reduction of H-reflex amplitude was observed during MI. These findings suggest that MI has modulatory effects on the spinal neuronal network. Specifically, the activation of low-threshold spinal structures during specific conditions (lengthening and H-reflex conditioning) highlights the possible generation of subliminal cortical output during MI.
ISSN:0022-3077
1522-1598
DOI:10.1152/jn.00952.2015