title: Anodal transcranial direct current stimulation of the motor cortex induces opposite modulation of reciprocal inhibition in wrist extensor and flexor.
abstract: Transcranial direct current stimulation (tDCS) is used as a noninvasive tool to modulate brain excitability in humans. Recently, several studies have demonstrated that tDCS applied over the motor cortex also modulates spinal neural network excitability and therefore can be used to explore the corticospinal control acting on spinal neurons. Previously, we showed that reciprocal inhibition directed to wrist flexor motoneurons is enhanced during contralateral anodal tDCS, but it is likely that the corticospinal control acting on spinal networks controlling wrist flexors and extensors is not similar. The primary aim of the study was to explore the effects of anodal tDCS on reciprocal inhibition directed to wrist extensor motoneurons. To further examine the supraspinal control acting on the reciprocal inhibition between wrist flexors and extensors, we also explored the effects of the tDCS applied to the ipsilateral hand motor area. In healthy volunteers, we tested the effects induced by sham and anodal tDCS on reciprocal inhibition pathways innervating wrist muscles. Reciprocal inhibition directed from flexor to extensor muscles and the reverse situation, i.e., reciprocal inhibition, directed from extensors to flexors were studied in parallel with the H reflex technique. Our main finding was that contralateral anodal tDCS induces opposing effects on reciprocal inhibition: it decreases reciprocal inhibition directed from flexors to extensors, but it increases reciprocal inhibition directed from extensors to flexors. The functional result of these opposite effects on reciprocal inhibition seems to favor wrist extension excitability, suggesting an asymmetric descending control onto the interneurons that mediate reciprocal inhibition.
authors.affiliation: Sorbonne Universités UPMC Université Paris 06, ER 6, F-75005, Paris, France; alexandra.lackmy@upmc.fr.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Lackmy-Vallée
authors.affiliation: Sorbonne Universités UPMC Université Paris 06, ER 6, F-75005, Paris, France; Faculty of Physical Therapy, Mahidol University, Nakonpathom, Thailand;
authors.forename: Wanalee
authors.initials: W
authors.lastname: Klomjai
authors.affiliation: APHP Hôpital Raymond-Poincaré-Service d'Explorations Fonctionnelles, Garches, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Bussel
authors.affiliation: Sorbonne Universités UPMC Université Paris 06, ER 6, F-75005, Paris, France; Faculty of Physical Therapy, Mahidol University, Nakonpathom, Thailand; Université de Versailles-Saint-Quentin, EA 4497, Garches, France; APHP Groupe Hospitalier Pitié-Salpêtrière-Service de Médecine Physique et Réadaptation, Paris, France; and.
authors.forename: Rose
authors.initials: R
authors.lastname: Katz
authors.affiliation: Université de Versailles-Saint-Quentin, EA 4497, Garches, France; APHP Groupe Hospitalier Pitié-Salpêtrière-Service de Médecine Physique et Réadaptation, Paris, France; and APHP Hôpital Raymond-Poincaré-Service d'Explorations Fonctionnelles, Garches, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Roche
mesh_terms: D000328:Adult; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000166:cytology / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D009433:Neural Inhibition; D011712:Pyramidal Tracts / Q000166:cytology / Q000502:physiology; D065908:Transcranial Direct Current Stimulation; D014953:Wrist / Q000294:innervation* / Q000502:physiology
keywords: human; motor cortex; spinal cord