title: Reproducibility of psychophysics and electroencephalography during offset analgesia.
abstract: BACKGROUND
  Offset analgesia (OA) is a pain-inhibiting mechanism, defined as a disproportionately large decrease in pain perception in response to a discrete decrease in noxious stimulus intensity. Hence, the aims were (1) to investigate whether psychophysics and electroencephalography (EEG) can be assessed simultaneously during OA and (2) to assess whether OA is reproducible within the same day as well as between different days.
  
  
  METHODS
  Two separate studies investigated OA: Study I (13 healthy volunteers; seven men; 25.5 ± 0.65 years) aimed at determining the feasibility of recording psychophysics and EEG simultaneously during OA. Study II (18 healthy volunteers; 12 men; 34 ± 3.15 years) assessed reproducibility of OA in terms of psychophysics and EEG. Subjects were presented to a 30-s OA heat stimulus paradigm on the volar forearm and psychophysics, and EEG recordings were obtained throughout the procedure. Reproducibility was assessed within the same day and between different days, using intraclass correlation coefficients (ICCs). Additionally, the reproducible psychophysical parameters were correlated to relevant EEG frequency bands.
  
  
  RESULTS
  Simultaneous recording of psychophysics and EEG affects the frequency distribution in terms of alpha suppression. Reproducibility was proven for the psychophysics and EEG frequency bands both within the same day (all ICCs > 0.62) and between different days (all ICCs > 0.66, except for the delta band). Correlations between psychophysics and EEG were found in the theta (4-8 Hz), alpha (8-12 Hz) and gamma (32-80 Hz) bands (all p < 0.01).
  
  
  CONCLUSIONS
  OA is a robust and reproducible model for experimental pain research, making it suitable for future research.
authors.affiliation: Mech-Sense, Department of Gastroenterology and Hepatology, Aalborg University Hospital, Denmark; Center for Sensory-Motor Interactions (SMI), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Nilsson
authors.forename: A
authors.initials: A
authors.lastname: Piasco
authors.forename: T D
authors.initials: TD
authors.lastname: Nissen
authors.forename: C
authors.initials: C
authors.lastname: Graversen
authors.forename: P
authors.initials: P
authors.lastname: Gazerani
authors.forename: M-F
authors.initials: MF
authors.lastname: Lucas
authors.forename: A
authors.initials: A
authors.lastname: Dahan
authors.forename: A M
authors.initials: AM
authors.lastname: Drewes
authors.forename: C
authors.initials: C
authors.lastname: Brock
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D004569:Electroencephalography / Q000379:methods / Q000592:standards*; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D010146:Pain / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods / Q000592:standards*; D058748:Pain Perception / Q000502:physiology*; D011601:Psychophysics / Q000379:methods / Q000592:standards; D015203:Reproducibility of Results