title: Intraoperative spinal cord monitoring using low intensity transcranial stimulation to remove post-activation depression of the H-reflex.
abstract: OBJECTIVE
  To investigate whether low intensity transcranial electrical stimulation (TES) can be used to condition post-activation depression of the H-reflex and simultaneously monitor the integrity of spinal motor pathways during spinal deformity correction surgery.
  
  
  METHODS
  In 20 pediatric patients undergoing corrective surgery for spinal deformity, post-activation depression of the medial gastrocnemius H-reflex was initiated by delivering two pulses 50-125ms apart, and the second H-reflex was conditioned by TES.
  
  
  RESULTS
  Low intensity TES caused no visible shoulder or trunk movements during 19/20 procedures and the stimulation reduced post-activation depression of the H-reflex. The interaction was present in 20/20 patients and did not diminish throughout the surgical period. In one case, the conditioning effect was lost within minutes of the disappearance of the lower extremity motor evoked potentials.
  
  
  CONCLUSIONS
  Post-activation depression was used to detect the arrival of a subthreshold motor evoked potential at the lower motor neuron. The interaction produced minimal movement within the surgical field and remained stable throughout the surgical period.
  
  
  CONCLUSIONS
  This is the first use of post-activation depression during intraoperative neurophysiological monitoring to directly assess the integrity of descending spinal motor pathways.
authors: Department of Physiology, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada.
authors: Jennifer C
authors: JC
authors: Andrews
authors: Department of Physiology, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada.
authors: Richard B
authors: RB
authors: Stein
authors: Department of Physical Education and Recreation, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada.
authors: Kelvin E
authors: KE
authors: Jones
authors: Department of Surgery, University of Alberta, Edmonton, Canada.
authors: Douglas M
authors: DM
authors: Hedden
authors: Division of Orthopaedic Surgery, University of Alberta, Edmonton, Canada.
authors: James K
authors: JK
authors: Mahood
authors: Division of Orthopaedic Surgery, University of Alberta, Edmonton, Canada.
authors: Marc J
authors: MJ
authors: Moreau
authors: Division of Orthopaedic Surgery, University of Alberta, Edmonton, Canada.
authors: Eric M
authors: EM
authors: Huang
authors: Department of Surgery, University of Alberta, Edmonton, Canada; Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Canada. Electronic address: francois.roy@ualberta.ca.
authors: François D
authors: FD
authors: Roy
mesh_terms: D000293:Adolescent; D002648:Child; D019054:Evoked Potentials, Motor; D005260:Female; D006181:H-Reflex; D006801:Humans; D008297:Male; D016343:Monitoring, Intraoperative / Q000379:methods*; D019635:Neurosurgical Procedures / Q000379:methods*; D013116:Spinal Cord / Q000502:physiology* / Q000601:surgery; D065908:Transcranial Direct Current Stimulation
keywords: H-reflex; Intraoperative monitoring; Motor evoked potential; Post-activation depression; Scoliosis; Spinal cord