title: Neural correlates of heterotopic facilitation induced after high frequency electrical stimulation of nociceptive pathways.
abstract: BACKGROUND
  High frequency electrical stimulation (HFS) of primary nociceptive afferents in humans induce a heightened sensitivity in the surrounding non-stimulated skin area. Several studies suggest that this heterotopic effect is the result of central (spinal) plasticity. The aim of this study is to investigate HFS-induced central plasticity of sensory processing at the level of the brain using the electroencephalogram (EEG). To this end we measured evoked potentials in response to noxious electrical pinprick-like stimuli applied in the heterotopic skin area before, directly after and 30 minutes after HFS.
  
  
  RESULTS
  We observed potential cortical electrophysiological correlates of heterotopic facilitation. Two different cortical correlates were found; the first one was a lateralized effect, i.e. a larger N100 amplitude on the conditioned arm than the control arm 30 minutes after end of HFS. This was comparable with the observed lateralized effect of visual analogue scale (VAS) scores as response to the mechanical punctate stimuli. The second correlate seems to be a more general (non-lateralized) effect, because the result affects both arms. On average for both arms the P200 amplitude increased significantly 30 minutes after end of HFS with respect to baseline.
  
  
  CONCLUSIONS
  We suggest that for studying heterotopic nociceptive facilitation the evoked brain response is suitable and relevant for investigating plasticity at the level of the brain and is perhaps a more sensitive and reliable marker than the perceived pain intensity (e.g. VAS).
authors.affiliation: Department of Anesthesiology, Pain & Palliative Medicine, Pain & Nociception Neuroscience Research Group, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. E.vandenbroeke@anes.umcn.nl
authors.forename: Emanuel N
authors.initials: EN
authors.lastname: van den Broeke
authors.forename: Casper H
authors.initials: CH
authors.lastname: van Heck
authors.forename: Clementina M
authors.initials: CM
authors.lastname: van Rijn
authors.forename: Oliver Hg
authors.initials: OH
authors.lastname: Wilder-Smith
mesh_terms: D000328:Adult; D001519:Behavior / Q000502:physiology; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D018913:Event-Related Potentials, P300 / Q000502:physiology; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D009619:Nociceptors / Q000502:physiology*; D010147:Pain Measurement; D010812:Physical Stimulation; D055815:Young Adult