title: Single-sweep spectral analysis of contact heat evoked potentials: a novel approach to identify altered cortical processing after morphine treatment.
abstract: OBJECTIVE
  The cortical response to nociceptive thermal stimuli recorded as contact heat evoked potentials (CHEPs) may be altered by morphine. However, previous studies have averaged CHEPs over multiple stimuli, which are confounded by jitter between sweeps. Thus, the aim was to assess single-sweep characteristics to identify alterations induced by morphine.
  
  
  METHODS
  In a crossover study 15 single-sweep CHEPs were analyzed from 62 electroencephalography electrodes in 26 healthy volunteers before and after administration of morphine or placebo. Each sweep was decomposed by a continuous wavelet transform to obtain normalized spectral indices in the delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (12-32 Hz) and gamma (32-80 Hz) bands. The average distribution over all sweeps and channels was calculated for the four recordings for each volunteer, and the two recordings before treatments were assessed for reproducibility. Baseline corrected spectral indices after morphine and placebo treatments were compared to identify alterations induced by morphine.
  
  
  RESULTS
  Reproducibility between baseline CHEPs was demonstrated. As compared with placebo, morphine decreased the spectral indices in the delta and theta bands by 13% (P = 0.04) and 9% (P = 0.007), while the beta and gamma bands were increased by 10% (P = 0.006) and 24% (P = 0.04).
  
  
  CONCLUSIONS
  The decreases in the delta and theta band are suggested to represent a decrease in the pain specific morphology of the CHEPs, which indicates a diminished pain response after morphine administration. Hence, assessment of spectral indices in single-sweep CHEPs can be used to study cortical mechanisms induced by morphine treatment.
authors.affiliation: Mech-Sense, Department of Radiology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Tine M
authors.initials: TM
authors.lastname: Hansen
authors.affiliation: Mech-Sense, Department of Gastroenterology & Hepatology, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Carina
authors.initials: C
authors.lastname: Graversen
authors.affiliation: Mech-Sense, Department of Radiology, Aalborg University Hospital, Aalborg, Denmark.|Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.
authors.forename: Jens B
authors.initials: JB
authors.lastname: Frøkjaer
authors.affiliation: Mech-Sense, Department of Gastroenterology & Hepatology, Aalborg University Hospital, Aalborg, Denmark.|Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anne E
authors.initials: AE
authors.lastname: Olesen
authors.affiliation: Division of Neurology, Ospedale Pediatrico Bambino Gesù, IRCCS, Rome, Italy.|Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Valeriani
authors.affiliation: Mech-Sense, Department of Gastroenterology & Hepatology, Aalborg University Hospital, Aalborg, Denmark.|Department of Clinical Medicine, Aalborg University, Aalborg, Denmark.|Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
authors.forename: Asbjørn M
authors.initials: AM
authors.lastname: Drewes
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000008:administration & dosage* / Q000009:adverse effects; D058256:Brain Waves / Q000187:drug effects*; D002540:Cerebral Cortex / Q000187:drug effects* / Q000502:physiology; D018592:Cross-Over Studies; D003718:Denmark; D004311:Double-Blind Method; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects*; D005260:Female; D064368:Healthy Volunteers; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009020:Morphine / Q000008:administration & dosage* / Q000009:adverse effects; D059225:Nociception / Q000187:drug effects*; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013697:Thermosensing / Q000187:drug effects*; D013997:Time Factors; D055815:Young Adult
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine
keywords: contact heat; electroencephalography; evoked brain potentials; morphine; spectral analysis