title: Enhanced short-term sensitization of facial compared with limb heat pain.
abstract: Habituation and sensitization are important features of individual sensitivity to repetitive noxious stimulation and have been investigated in numerous studies. However, it is unclear whether these phenomena vary depending on the site of stimulation. Here we compared short-term and long-term effects of painful heat stimulation on the forehead and limb using an established longitudinal heat pain paradigm performed over 8 consecutive days in 36 healthy volunteers. Participants were randomized into 2 groups; participants received repetitive heat pain stimulation either on the left volar forearm or on the left side of the forehead. Our data show a comparable degree of habituation over the course of 8 days in both groups. However, participants in the trigeminal stimulation group exhibited stronger within-session sensitization (indexed by a higher within-session increase in pain intensity ratings) than those who received the forearm stimulation. Furthermore, over the course of the experiment we found a correlation between habituation and anxiety, showing less habituation in participants with higher trait anxiety scores. Our findings are in line with somatotopic differences in response to painful stimulation and a higher proneness of trigeminal pain to sensitization processes, which might be explained by the biological relevance of the head and facial area for vital functions. The contribution of this sensitivity to the development and maintenance of clinical facial pain and headache disorders warrants further investigation.
  
  
  CONCLUSIONS
  This study uses psychophysical methods to evaluate the differences in long-term habituation and short-term sensitization to heat pain between the trigeminal and spinal systems. We found stronger sensitization for trigeminal compared with nociceptive stimuli on the forearm. The contribution of this sensitivity to clinical pain states warrants further investigation.
authors.affiliation: University Hospital Essen, University of Duisburg-Essen, Essen, Germany; University Medical Center Hamburg-Eppendorf, University of Hamburg, Hamburg, Germany. Electronic address: katharina.schmidt@uk-essen.de.
authors.forename: Katharina
authors.initials: K
authors.lastname: Schmidt
authors.affiliation: University Medical Center Hamburg-Eppendorf, University of Hamburg, Hamburg, Germany.
authors.forename: Odette
authors.initials: O
authors.lastname: Schunke
authors.affiliation: University Hospital Essen, University of Duisburg-Essen, Essen, Germany.
authors.forename: Katarina
authors.initials: K
authors.lastname: Forkmann
authors.affiliation: University Hospital Essen, University of Duisburg-Essen, Essen, Germany; University Medical Center Hamburg-Eppendorf, University of Hamburg, Hamburg, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Bingel
mesh_terms: D000328:Adult; D005121:Extremities / Q000294:innervation*; D005145:Face / Q000294:innervation*; D005239:Fear / Q000523:psychology; D005260:Female; D006185:Habituation, Psychophysiologic; D064368:Healthy Volunteers; D006358:Hot Temperature / Q000009:adverse effects*; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology* / Q000523:psychology; D008297:Male; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D011601:Psychophysics; D011897:Random Allocation; D013223:Statistics as Topic; D011795:Surveys and Questionnaires; D013997:Time Factors; D055815:Young Adult
keywords: Trigeminal pain; experimental pain; habituation; heat pain; sensitization