title: Spinal associative stimulation: a non-invasive stimulation paradigm to modulate spinal excitability.
abstract: OBJECTIVE
  Repetitive, paired peripheral and transcranial stimulation targeting the cerebral cortex can increase cortical excitability, outlasting the stimulation period. It is unknown whether paired stimulation specifically targeting the spinal cord can modulate spinal excitability. We tested whether the H-reflex facilitation from a sub-threshold conditioning TMS pulse could modulate spinal excitability if delivered repetitively.
  
  
  METHODS
  In 13 healthy subjects, we delivered single-pulse TMS (80% RMT) for the right soleus muscle, 20 ms prior to an electrical peripheral nerve stimulus delivered over the posterior tibial nerve on the same side at 0.1 Hz during 15 min.
  
  
  RESULTS
  PNS alone evoked an H-reflex of 0.25 mV ± 0.06 SEM, while pairing of TMS and PNS facilitated the H-reflex to 0.7 ± 0.11 mV. TMS-PNS pairs delivered at 0.1 Hz for 15 min progressively increased in the evoked response to ∼130% (r(2) = 0.97) of the starting amplitude (normalized to 1st min). Post-intervention, H-reflex threshold decreased (pre = 12.9 ± 1.7 mA; post =11.6 ± 1.6 mA; p = 0.04), as did the stimulus intensity at maximum H-reflex amplitude (pre = 23.5 ± 02.8 mA; post = 21.6 ± 2.6 mA; p = 0.03), and recruitment curve width (pre = 11.6 ± 1.5 mA; post = 10.93 ± 1.4 mA; p = 0.03). No such changes were observed with intervention of PNS or TMS alone.
  
  
  CONCLUSIONS
  Paired stimulation targeting spinal facilitatory interactions, when applied repetitively, can increase spinal excitability during and after the intervention.
  
  
  CONCLUSIONS
  Spinal associative stimulation may have potential for neuromodulation in spinal cord injury patients.
authors.affiliation: Winifred Masterson Burke Medical Research Institute, White Plains, NY, USA.
authors.forename: Mar
authors.initials: M
authors.lastname: Cortes
authors.forename: Gary W
authors.initials: GW
authors.lastname: Thickbroom
authors.forename: Josep
authors.initials: J
authors.lastname: Valls-Sole
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.forename: Dylan J
authors.initials: DJ
authors.lastname: Edwards
mesh_terms: D000293:Adolescent; D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D003430:Cross-Sectional Studies; D004525:Efferent Pathways / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000502:physiology*; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult