title: Independent modulation of corticospinal and group I afferents pathways during upright standing.
abstract: Balance control during upright standing is accompanied by an increased amplitude of motor-evoked potentials (MEP) induced by transcranial magnetic stimulation and a decreased amplitude of the Hoffmann (H) reflex in the soleus muscle. Nonetheless, whether these observations reflect reciprocal adjustments between corticospinal and group I afferents pathways during upright standing remains unknown. To further investigate this question, cathodal transcranial direct current stimulation (c-tDCS) applied over the motor cortex and vibration of Achilles tendons were used to modify the excitability of corticospinal and group I afferent pathways, respectively. MEPs and H reflexes were recorded in the soleus muscle during upright standing with or without bilateral Achilles tendon vibration, these recordings being performed before and after 20 min of c-tDCS (1.5 mA) or sham stimulation applied over the sensorimotor cortex. The results indicate that tendon vibration increased MEP amplitude (+28%) and decrease (-68%) the H-reflex amplitude (p<0.05). After c-tDCS, MEP amplitude was reduced by 13% and 26% without and with tendon vibration (p<0.05), respectively. In contrast, no significant change occurred in H-reflex amplitude after c-tDCS. Regardless of the conditions (c-tDCS and tendon vibration), no significant correlation was observed between changes in MEP and H-reflex amplitudes. The results failed to demonstrate close reciprocal changes in soleus MEP and H-reflex amplitudes during upright standing. These original findings suggest independent adjustments in corticospinal and group I afferents pathways during upright standing.
authors: Laboratory of Applied Biology, Neuroscience Institute, Université Libre de Bruxelles (ULB), 808 route de Lennik, 1070 Brussels, Belgium. Electronic address: sbaudry@ulb.ac.be.
authors: S
authors: S
authors: Baudry
authors: Laboratory of Applied Biology, Neuroscience Institute, Université Libre de Bruxelles (ULB), 808 route de Lennik, 1070 Brussels, Belgium.
authors: J
authors: J
authors: Duchateau
mesh_terms: D000125:Achilles Tendon / Q000502:physiology; D000328:Adult; D000344:Afferent Pathways / Q000502:physiology*; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D011187:Posture / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: H reflex; balance; tendon vibration; transcranial direct current stimulation (tDCS); transcranial magnetic stimulation; upright standing