title: Chemo-somatosensory evoked potentials: a sensitive tool to assess conditioned pain modulation?
abstract: Abstract Background: Chemo-somatosensory evoked potentials (CSSEPs) elicited by chemical stimulation (CO₂ gas) of the nasal mucosa have been shown to be sensitive enough to pick up even weak analgesic effects. With the present study we wanted to investigate whether CSSEPs are also a sensitive tool to capture endogenous pain inhibitory mechanisms elicited by conditioned pain modulation (CPM; where a first conditioning stimulus reduces the sensitivity for a second test stimulus) with a conditioning stimulus of rather low noxious load.
  
  
  METHODS
  Seventeen healthy participants were tested for CPM effects (conditioning stimulus: tonic heat pain with intensities around the pain threshold induced via a thermode; test stimulus: chemonasal stimulation (73% and 78% CO₂)) on CSSEPs and on self-report ratings.
  
  
  RESULTS
  We found significant CPM effects in the CSSEPS, with reduced amplitudes and prolonged latencies at several electroencephalogram (EEG) recording positions when using the lower CO₂ concentration (73% CO₂). In contrast to the visible inhibitory effects on the CSSEPs, subjective ratings of the test stimulus did not reflect CPM action.
  
  
  CONCLUSIONS
  The experimental pain model using CO₂ stimuli to elicit CSSEPs proved to be sensitive enough to capture weak CPM effects elicited by a conditioning stimulus of rather low noxious load. The usage of such mild noxious conditioning stimuli-in contrast to stimuli of higher noxious load (e.g., cold pressor test)-has the advantage that the activation of other types of pain inhibitory mechanisms in parallel (like attentional distraction, stress-induced analgesia) can be avoided.
authors.affiliation: Physiological Psychology, Otto-Friedrich University , Bamberg , Germany and.
authors.forename: Miriam
authors.initials: M
authors.lastname: Kunz
authors.forename: Parvaneh
authors.initials: P
authors.lastname: Mohammadian
authors.forename: Bertold
authors.initials: B
authors.lastname: Renner
authors.forename: Stephan
authors.initials: S
authors.lastname: Roscher
authors.forename: Gerd
authors.initials: G
authors.lastname: Kobal
authors.forename: Stefan
authors.initials: S
authors.lastname: Lautenbacher
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000009:adverse effects; D003213:Conditioning, Psychological; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D011601:Psychophysics; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: Chemo-somatosensory evoked potentials; conditioned pain modulation; experimental pain; weak noxious load