title: Principle components analysis of pain thresholds to thermal, electrical, and mechanical stimuli suggests a predominant common source of variance.
abstract: We addressed the question whether pain thresholds to different stimuli measure independent aspects of pain or one common phenomenon. In the first case, different stimuli are required to completely characterize a subject's pain sensitivity. In the second case, different stimuli are redundant and can be used to calculate composite scores across pain modalities. We measured pain thresholds to several stimuli (heat, heat/capsaicin, cold, cold/menthol, blunt pressure, 5-Hz sine-wave electric current (0-20mA), punctate pressure (von Frey hairs), and von Frey hairs plus capsaicin application) in 45 healthy men and 32 healthy women (aged 20-44 years). We observed that pain thresholds were significantly correlated with each other. Principal component analysis indicated that their variance was attributable more to the difference in subjects (variance estimate: 0.393) than to the difference in pain stimuli within a subject (variance estimate: -0.008). Among three principal components of the intercorrelation matrix with eigenvalues >1, the first, explaining 48% of the total variance, carried high loadings from all stimuli indicating that they shared a common source of half of their variance. Only minor variance components, each explaining <14% of the total variance, indicated a distinction of pain stimuli. There, a pattern of similarities and dissimilarities emerged agreeing with known distinct mechanisms of nociceptive responses to different stimuli. We conclude that characterizing a person as being generally stoical or complaining to any painful stimulus appears to be justified at least at pain threshold level.
authors.affiliation: pharmazentrum frankfurt/ZAFES, Institute of Clinical Pharmacology, Johann Wolfgang Goethe-University, Theodor Stern Kai 7, D-60590 Frankfurt am Main, Germany.
authors.forename: Till J
authors.initials: TJ
authors.lastname: Neddermeyer
authors.forename: Karin
authors.initials: K
authors.lastname: Flühr
authors.forename: Jörn
authors.initials: J
authors.lastname: Lötsch
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000009:adverse effects; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology / Q000523:psychology; D008297:Male; D010146:Pain / Q000139:chemically induced / Q000503:physiopathology* / Q000523:psychology*; D010147:Pain Measurement / Q000379:methods* / Q000592:standards; D017288:Pain Threshold / Q000502:physiology* / Q000523:psychology*; D010812:Physical Stimulation / Q000009:adverse effects; D025341:Principal Component Analysis / Q000379:methods*