title: New evidence of corticospinal network modulation induced by motor imagery.
abstract: 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.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U1093, Faculté des sciences du sport, Dijon, France; and Université de Bourgogne Franche-Comté, Besançon, France sidney.grospretre@univ-fcomte.fr.
authors.forename: Sidney
authors.initials: S
authors.lastname: Grosprêtre
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U1093, Faculté des sciences du sport, Dijon, France; and Université de Bourgogne Franche-Comté, Besançon, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Lebon
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U1093, Faculté des sciences du sport, Dijon, France; and Université de Bourgogne Franche-Comté, Besançon, France.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Papaxanthis
authors.affiliation: Institut National de la Santé et de la Recherche Médicale U1093, Faculté des sciences du sport, Dijon, France; and Université de Bourgogne Franche-Comté, Besançon, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
mesh_terms: D019054:Evoked Potentials, Motor; D006181:H-Reflex; D006801:Humans; D007092:Imagination; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D011597:Psychomotor Performance; D011712:Pyramidal Tracts / Q000502:physiology*; D055815:Young Adult
keywords: H-reflex; cervico-medullar-evoked potential; motor-evoked potential; muscle lengthening; presynaptic inhibition; transcranial magnetic stimulation