title: Altered cortical responsiveness to pain stimuli after high frequency electrical stimulation of the skin in patients with persistent pain after inguinal hernia repair.
abstract: BACKGROUND
  High Frequency electrical Stimulation (HFS) of the skin induces enhanced brain responsiveness expressed as enhanced Event-Related Potential (ERP) N1 amplitude to stimuli applied to the surrounding unconditioned skin in healthy volunteers. The aim of the present study was to investigate whether this enhanced ERP N1 amplitude could be a potential marker for altered cortical sensory processing in patients with persistent pain after surgery.
  
  
  METHODS
  Nineteen male patients; 9 with and 10 without persistent pain after inguinal hernia repair received HFS. Before, directly after and thirty minutes after HFS evoked potentials and the subjective pain intensity were measured in response to electric pain stimuli applied to the surrounding unconditioned skin.
  
  
  RESULTS
  The results show that, thirty minutes after HFS, the ERP N1 amplitude observed at the conditioned arm was statistically significantly larger than the amplitude at the control arm across all patients. No statistically significant differences were observed regarding ERP N1 amplitude between patients with and without persistent pain. However, thirty minutes after HFS we did observe statistically significant differences of P2 amplitude at the conditioned arm between the two groups. The P2 amplitude decreased in comparison to baseline in the group of patients with pain.
  
  
  CONCLUSIONS
  The ERP N1 effect, induced after HFS, was not different between patients with vs. without persistent pain. The decreasing P2 amplitude was not observed in the patients without pain and also not in the previous healthy volunteer study and thus might be a marker for altered cortical sensory processing in patients with persistent pain after surgery.
authors.affiliation: Department of Anesthesiology, Pain & Palliative Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Emanuel N
authors.initials: EN
authors.lastname: van den Broeke
authors.affiliation: Department of Surgery, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Lonneke
authors.initials: L
authors.lastname: Koeslag
authors.affiliation: Department of Anesthesiology, Pain & Palliative Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Arendsen
authors.affiliation: Department of Surgery, Catherina Hospital, Eindhoven, The Netherlands.
authors.forename: Simon W
authors.initials: SW
authors.lastname: Nienhuijs
authors.affiliation: Department of Surgery, Canisius-Wilhelmina Hospital, Nijmegen, The Netherlands.
authors.forename: Camiel
authors.initials: C
authors.lastname: Rosman
authors.affiliation: Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, Nijmegen, The Netherlands.
authors.forename: Clementina M
authors.initials: CM
authors.lastname: van Rijn
authors.affiliation: Department of Anesthesiology, Pain & Palliative Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Oliver H G
authors.initials: OH
authors.lastname: Wilder-Smith
authors.affiliation: Department of Surgery, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Harry
authors.initials: H
authors.lastname: van Goor
mesh_terms: D000328:Adult; D000368:Aged; D001519:Behavior; D002540:Cerebral Cortex / Q000503:physiopathology*; D003213:Conditioning, Psychological; D003710:Demography; D004558:Electric Stimulation; D005071:Evoked Potentials; D006552:Hernia, Inguinal / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D017288:Pain Threshold; D010149:Postoperative Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D012867:Skin / Q000503:physiopathology*; D011795:Surveys and Questionnaires; D014945:Wound Healing